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RELIEF VALVE LEAKS
RESET SWITCH, HEATER PRIMARY CONTROL
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SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
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THERMOSTATS, HEATING / COOLING
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WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
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ZONE VALVES, HEATING
Best settings for a heating boiler aquastat control:
Here we explain how to choose the best settings for a heating boiler aquastat - the combination control that sets boiler temperature and may also control hot water production via a tankless coil on the heating boiler.
We also give advice on how to set the aquastat controls if heating with a woodstove.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
After explaining the Hi, Lo, and Diff controls we review the newer universal replacement aquastat from Honeywell, the L7224U Universal Aquastat, followed by a discussion of the simpler single-limit control switches.
At AQUASTAT CONTROL Functions we explain how aquastats work, defining the functions and dials of the aquastat HI LO and DIFF control along with the reset button often found on these heating boiler controls.
This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
The photo above shows a the "HIGH" or "HI" setting on a Honeywell R8124A combination heating control, also called an "aquastat". Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
The internal view of the Honeywell R8182D (left) can be found along with additional details about this control in the Honeywell R8182D,H Combination Protectorelay™ Primary Control and Aquastat® Controller Installation Instructions (link to copy below at REFERENCES).
Following wiring details in the instruction manual, the R8182D,H can replace other aquastat controls such as the Tradeline R8182B, R8182E, R8182F, R8182H, R8182J, or White Rogers 6C92.
Lots of people, even some service technicians are confused about the actual function of combination controls and aquastats like the Honeywell R8182D. Some don't know how to set the "HI", "LO" and "DIFF" dials on a combination control.
Or more commonly, we were taught to just use a "rule of thumb" which set the
These were "Safe" settings for this control, and it's in with similar settings on millions of heating boilers. But with a little thought, we can adjust these HI LO DIFF settings and thus set the heating aquastat control so as to save a bit more on heating cost, and/or we can set the control to give us a bit more hot water where a tankless coil is installed.
Guide to Best Settings for the HI Limit on a Honeywell R8182D Heating Boiler Aquastat & Similar Controls:
The "HI" on a combination heating control like this aquastat is usually set by the heating service technician to a spot between 180 °F and 200 °F. Or the "rule of thumb" fellows just park it at about "180" °F as you can see in our photo.
Setting the HI: save money on heating costs by running the boiler at a higher temperature
Generally a heating boiler is more efficient if we operate it at a higher temperature.
The thermal conductivity of heating water inside of finned copper tubing baseboards or through radiator surfaces is exponentially greater at higher temperatures.
In other words, hotter water actually transfers heat into the occupied space more efficiently than cooler water.
Since this is not lab-grade equipment these settings are not precisely accurate. For this reason we like to set our HI limit at around 200 °F.
We let the boiler run through a few heating cycles, watching the temperature and pressure gauges on the boiler to see what temperature we're actually reaching. And we watch the boiler relief valve to be sure we're not causing leakage there.
Watch out: Setting the "HI" too high on the aquastat can result in over-temperature in the heating boiler and can result in dumping water and temperature and pressure at the relief valve. If your TP valve was not leaking before and it begins to drip when you set up the HI to 200 F, step the HI back to 195 and try that setting.
If your TP valve is leaking at 195 or less it's likely that you need a heating service call - something's probably wrong with the relief valve, with system operating pressures, or with the controls.
Guide to Best Settings for the "LO" Limit on a Honeywell R8182D Heating Boiler Aquastat & Similar Controls:
In our photo at left you'll see where the heating service tech left this "LO" limit control after cleaning and tuning the heating boiler.
The "LO" is set at least 20 deg F. below the "HI" limit on a combination control.
If we set the "LO" any closer top "HI" it is possible that the control, trying to give priority to making domestic hot water for someone in the shower, will simply lock out the circulator pump entirely - the heating circulator will never run.
Your heat will work, but slowly, and more expensively, as we explain below at Circulator Lockout.
We like to keep our LO set at 20 F below the HI. That keeps the LO temperature operating range as high as possible in the boiler and that in turn gives us the most heat stored in the boiler for making hot water through the tankless coil.
What happens if you "cross the controls" and set "LO" above "HI" or if you set "LO" too close to "HI"? The circulator will not run.
Watch out: don't set the LO above or higher than the HI temperature limit. If you make that mistake, you will lock out the circulator pump and your heating system will not work properly. We call this "lock out" - the circulator will be locked out of running on a call for heat. Others call this LO higher than HI "crossed controls".
We've inspected homes at which the owner, for decades, observed that the heat in the building was very slow to come up in response to the thermostat. The problem was that the LO was set close to or even above the HI - the circulator pump never ran and hot heating water circulated but only very slowly by convection.
We found a home where the owner had set the "HI" to 120 and the "LO" to 180. Luckily for them, because their flow-control valve was either absent or not working, their home would indeed receive heat - but very slowly: their circulator pump had never run. On seeing this setting we asked the owner about it. "Well you know", he said, "we have noticed that the house was always very slow to heat up in winter." Thanks to reader L. Clark for pointing out that we had inconsistent language in this explanation. It's been fixed, and fixed again thanks to reader Damian for suggesting further clarifications.
Guide to Setting the "DIFF" (differential) on a Honeywell R8182D heating boiler aquastat & Similar Controls:
Our photo (left) shows the DIFF adjustment on a Honeywell aquastat. This DIFF is set to its lowest value: 10 °F.
At the setting shown, if LO were set to 120, when the burner is re-heating the boiler water and water temperature rises to 130 F the burner will turn off and the heating circulator pumps will be allowed to turn on (and they will actually turn on if the room thermostat is calling for heat).
If you re-set the DIFF dial up to its maximum of 25 and LO remained at 120 F, then when the burner is re-heating the boiler water and water temperature rises to 145 F the burner will turn off and the heating circulator pumps will be allowed to turn on (and they will actually turn on if the room thermostat is calling for heat).
In short, DIFF = 25 should give you hotter boiler temperature and thus more domestic hot water than DIFF = 10.
Keep in mind that the LO and DIFF control settings only make sense if the heating boiler has a tankless coil installed to make domestic hot water (for washing and bathing). If your heating system does NOT include a tankless coil, the LO and DIFF are keeping heat in the boiler for a tankless coil that is not present and you could consider either disabling this circuit entirely or setting both LO and DIFF to their lowest settings. Details are at Disabling the LO and DIFF settings
Watch out: be sure that a mixing valve or anti-scalding valve is installed to avoid hot water burns as well as to make effective use of this higher boiler temperature.
For details about the HI, LO, and DIFF actually work, refer to our text and to the yellow-colored area in our colored version of the HI LO functions explained in detail at AQUASTAT CONTROL Functions in that article's section More about How the HI and LO Limit Controls Function on an Aquastat above. From that article, this quote helps explain what the DIFF control is doing on an aquastat:
It's not hard to understand why heating service techs and homeowners are confused about LO and DIFF settings on a heating boiler, but Honeywell got it right: if we are making hot water with a tankless coil, by locking out the circulator at lower boiler temperatures, the LO and DIFF make sure that heating priority is given to the woman in the shower, not to the building radiators.
[Click to enlarge any image] The diagram above is explained at AQUASTAT CONTROL Functions
Do You Want to Disable the LO and DIFF settings on a Boiler that Does Not Use a Tankless Coil for Domestic Hot Water?
If a tankless coil is not installed on a boiler where this combination aquastat control is installed, this combination control may still be in use. And that's not always desirable. It depends. In this case, the "LO" has almost no use whatsoever and, if you read the instructions provided by the control manufacturer you'll probably see that the manufacturer calls for the "LO" to be electrically disconnected entirely.
Details about how to make this change to a typical aquastat, along with problems to watch-out for have been moved to a new article found at AQUASTAT LO & DIFF DISABLED [Live link is given just below]
Continue reading at AQUASTAT LO & DIFF DISABLED or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: how to set the DIFF control
(Sept 2, 2011) Joe P. said:
(Sept 14, 2011) email@example.com said:
Joe, in our text above in discussing the DIFF setting, we stated:
Where a tankless coil is installed on a heating boiler to make domestic hot water (for washing and bathing) we prefer to set the differential (DIFF) to its highest number (usually 25 degrees).
But if you want the most hot water, you'll want to set the LO up as high as you can to keep the boiler hotter for making more and hotter water (storing more heat in the boiler). The highest you can set the LO is to 20 degrees BELOW the HI setting (to avoid circulator lockout).
If you set the LOW DOWN instead of UP then when you are not calling for heat the boiler will be kept at a comparably lower temperature and you'll have less hot water than otherwise.
Thanks for the question, I'll review our text again and adjust it for clarity as needed.
Question: wood burning heating boiler tied into oil fired heating boiler controls
(Oct 17, 2011) Phillip said:
I have just installed an outside wood burning furnace that ties into my oil Furnace via a water to water heat exchanger. The wood furnace cycles Hot water constantly. When the house calls for heat the oil furnace turns on for about 5 minutes or longer. I assume this a result of the colder radiator Water cycling through the heat exchanger.
Once the oil furnace gets up to temp it stops and the wood furnace keeps up. I would like to have the Oil furnace burner not turn on at all. Can I unplug the connector from the Aquastat to the burner? And will the two circulating pumps still work for the Hot water and heat.
(Dec 7, 2011) Jeff said:
I have just installed an outside wood burning furnace that ties into my oil
I agree that the shot of cold water from the home's radiators will drop temperature in the boiler and cause its burner to turn on.
If the system is wired as usual, if you disconnect electrical power to the oil burner itself the circulator pumps will continue to function normally, Phillip. In fact one could install an electrical switch just for that purpose.
Just watch out: if you leave the burner off and also leave the home such that your wood burner runs down you'll risk frozen pipe damage.
Here's an alternative to consider:
But if you temporarily drop the HI down to 120, the "ON" point will be around 100 - that too might prevent unnecessary boiler cycling when the wood burner is working.
If you do use a tankless coil and the aquastat's LO and DIFF are left in service be sure to also keep the LO set to at least 20 degF below the new HI setting.
(Oct 18, 2011) Phillip said:
Thanks DanJoeFriedman for the response. I have a one zone house with about 18 radiators. The amount of cold radiator water is quite large to cycle through the furnace. If I understand you correctly no matter what setting I use for the Hi/Lo and differential I would still expect that the oil furnace would kick in until the temp reached the diff limit. Today I set the hi to about 140 the low to 120 and the diff to 10 degrees. My thought was that with the lo set at 120 the furnace would kick off at about 130 degrees and with the heat exchanger helping out heat the cold return water that that would minimize the amount of time the oil furnace is on.
Ideally I would like the oil burner to never kick on unless the wood furnace burns out or has a failure with its circulating pump. If there is no harm in just unconnecting the burner cable from the aquastat (there is a nice connector in the middle of the cable) then I might try that this weekend. I can always reconnect during the cold months as a backup. So just to be clear on a typical installation there is no feadback to the Aquastat from the burner unit that would cause the Aquastat from not turning on the circulating pumps when there is a call fro heat from the house or the hot water tank?
Not quite Phillip
Please review the explanation of HI LO DIFF
The boiler will start it's oil burner if on a call for heat at the thermosta the boiler temp is about 10F below the HI
The Lo and diff settings maintain heat in the boiler when there is no call for heating, in order to heat a tankless coil in summer.
I'm skipping details found in the articlesnon this topic.
Question: How to stop using the tankless coil
(Oct 27, 2011) Marc Ruland said:
I stopped using the tankless coil for domestic water last year upon having a large external tank installed (smart 40 system). I read the above article describing a disconnect of the low setting. Wouldn't that be a bad idea for winter heating as the house would call for heat and the furnace would run and run to try and bring the base boards up to temp.? Also is there a more efficeint system or way to run my current system for winter. As it is now with my Weil-McLain Oil Boiler at Hi 200 Low 160 my furnace runs almost every 15 minutes. Is that just the way it's supposed to work? Each new winter season I always seem to forget how much that thing runs and oil isn't getting any cheaper.
(Nov 17, 2011) Josh said:
Take a look at the instructions found in AQUASTAT LO & DIFF DISABLED if you want to abandon using a tankless coil
Question: Burnham oil boiler with a honeywell aquastat set at 180/160/20 diff
(Feb 15, 2012) Nick said:
Currently I have a Burnham oil boiler with a honeywell aquastat set at 180/160/20 diff. I am planning on installing an electric hot water heater in series with the boiler so that in the winter the coil is used to preheat the water coming into the electric hot water and in summer I can fully turn off the oil boiler and only rely on the electric hot water heater, thus using no oil but still having hot water. IN the winter, when I am using the boiler to heat the house- using copper/aluminum baseboards- what are going to be my best settings.
We tend to keep the house on the cool side, as this is a guest-house that isn't always occupied. We live in Maryland, so there are some very cold days, and some not so cold. My feeling is that settings along the lines of 190/120/25 diff might be good. It seems that the low should be set very low- on a warm winter day where there is minimal call for heat, there is no reason to keep the water warm, and everything suggests that the high should be high with this type of baseboard as it is much more efficient at a high temperature. My goal is to maximize efficiency, ie minimize oil usage. What are peoples' thoughts on this??? I'm unclear what my best diff setting is. Does the diff only effect the low?
(Feb 15, 2012) Nick said:
(Feb 28, 2012) Buddy said:
Nick, I installed an electric water heater in parallel with my tankless water heater last year. You can see my comments on January 12, 2012 on this web-site under "Guide to Heating System Boiler Aquastats (AQUASTAT CONTROL) , Their Settings & Wiring." Installing your electric water heater in series after the tankless seems to makes sense since your hot water usage is probably relatively low. My old settings were 190 hi/160 low/ 15 diff in order to ensure adequate domestic hot water temperature. This winter I have my Aquastat set at the lowest possible, 130 hi/ 110 low/ 10 diff although the actual boiler temperature seems to run about 150 hi and 120 low. I am using the electric water heater but not the tankless.
These settings have been adequate to re-heat the house with copper/aluminum finned baseboard and set-back thermostats set at 58 degrees night and 68 degrees daytime, while maintaining house temperature even on the coldest days. It does take longer to heat up the house now but the temp no longer swings up past the thermostat setting and rooms that ran colder than others before now seem to benefit from the lower boiler temperature and longer circulator run times. If your guest-house is well insulated you can probably get by with these settings. If not, you can always bump up the high temp.
The lower aquastat settings should save oil due to reduced heats loss out the flue and from the boiler casing and also from the higher heat transfer efficiency from the burner flame to the colder boiler water. The baseboard will now transfer less heat per hour per square foot at the lower temperature but the heat transfer efficiency will still be 100 percent. Efficiency will not change with water temperature, only the heat transfer rate. Unintended consequences - 1) The basement is now cooler in the summer and more humid. Running a dehumidifier may kill my savings. 2) The internal cast iron boiler sections may be more rapidly corroding due to not being heated.
(June 12, 2012) Paul said:
Nick, I have a Weil-Mclain Gold Oil Burner Model P-WTG04 series 3 boiler. I have 4 heats zones controlled by an Agro controller. I also have an Amtrol Boiler mate for hot water connected to the Argo priority zone. What should I set the Honeywell 8124 A aquastat. I am confused as the what differential and Low limit should be used, It is presently set 160 H 140 Low and 15% DIF. Thank you for your help!
(June 14, 2012) DanJoeFriedman (mod) said:
Nick, for reasons we explain in the article above, we don't prefer your aquastat settings for a boiler that includes a tankless coil.
Buddy, thanks for the helpful detail and update.
On most points including your advice to Radhames, we agree completely. Contact me by email if you want to be more fully identified as a reviewer/commentator.
(Nov 13, 2012) Buddy said:
Question: Would the 200/180/25 diff settings still be the best
(July 5, 2012) Dan said:
Great article. I have a somewhat more unique situation that I could use your advice on for setting the aquastat. It's a newish burnham tankless coil burner, but in a summer home so the room heat is never turned on.
Would the 200/180/25 diff settings still be the best for maximizing hot water and minimizing energy consumption, or can you recommend more appropriate settings for a burner just used to heat the tankless coil for showers, etc?
Dan - good question. You're asking: if we never call for heat, just for hot water via a tankless coil on the boiler, do we still want those "high" settings on the aquastat?
The short answer is yes. You don't want to set the HIGH ever above 200 F as it risks overheating the boiler and spilling at the TP relief valve.
You want as much HOT water as you can get for washing and bathing. But if we never call for heat, the system is always going to operate off of the LO and the DIFF settings.
180 is as high as you can set the LO - since it has to be 20 degF below the HI should proper heating ever be needed in the future.
In sum, keep the settings high and use a mixing valve or tempering valve to avoid getting scalded in the shower.
At those settings when never calling for heat, the standby losses at the boiler are very small - since the controls and boiler only have to heat up the relatively small volume of water inside the boiler itself - not the water in heating baseboards or radiators.
Question: higher boiler aquastat settings vs outdoor air temperature sensors
(Sept 17, 2012) Bob said:
(Oct 18, 2012) Anonymous said:
So how does an outdoor air system save money if the water temperature is lowered down to 140,150, etc. and the thermal efficiency is lowered, according to the above?
Bob, thanks for the comment. I agree that those are two contrasting approaches operating under different principles. I'm not sure there is a true/false answer when different factors are at work. Generally, though, we learn in oil burner school that longer on cycles and higher water temperatures make for higher operating efficiency of the boiler and better heat transfer.
(Nov 7, 2012) Buddy said:
Regarding (Oct 18, 2012) Anonymous comment: The relationship between heating capacities (rate of heat transfer) and average hot water temperatures for copper aluminum-finned baseboards is actually linear and proportional. If you simply plot, on graph paper, the performance data (hot water temperatures vs. heat capacity ratings) provided by baseboard system manufacturers that follow the AHRI rating standards, you will see that the relationship is not exponential.
Simply stated, efficiency is defined as input divided by output. For a baseboard heater the term "efficiency" is actually a misnomer and should not used when discussing baseboard heat ratings. A baseboard heater merely transfers heat. The heat removed from the hot water is equal to the heat gained in the occupied space. There is no heat lost in this process. Thus, 100% of the heat is transferred. If the statement you quoted was a direct quote from a published source, I would be suspicious of any "technical" information furnished in that document.
The fuel savings produced by an ambient temperature reset system is apparently achieved by an improvement in the efficiency of the "total hydronic system" and not just one component. Evaluation of this phenomenon requires a complex analysis of burner cycle times, heat transfer from burner flame to heating water, stack losses, heat losses during burner and/or circulating pump on/off cycles, etc. and is not easily quantified or explained. I trust that the manufacturers are correct in their analyses and actual system field tests and that actual savings can be realized using a setback system.
I do not have the money to install a setback system. However, using available internet information to determine the appropriate reset temperatures, I merely adjust my boiler's high water temperature setting several times during the heating season based on the anticipated ambient temperatures and trust that I am achieving some amount of savings.
(Nov 5, 2012) Ron Walken said:
I have a 1925 cold boiler likely with a heavier heat exchanger. It is controled with High and low setting. It never has heated the usable hot water. After learning what I could three years ago when we purchased the place I got a honeywell 3 degree set thermostat because it was only achieving 120 degrees during a cycle. It now reaches 160 plus on a cycle.
I am thinking I would like to raise the low temp setting on the control unit in the winter months to 120. My thinking is that I could select a thermostat with a 1- 2 degree swing and the home would be consistently more comfortable.
Today it swings from 68 to 72. It has a natural gas burner a good circulating pump and is installed in the center of the main floor so all heat generated would stays within the structure.
Question: L6006C Aquastat to control blower for combustion on my outdoor coal boiler.
(Nov 17, 2012) Anonymous said:
Question: how much higher can I safely go on these aquastat settings?
(Jan 16, 2013) John B said:
You can't set the aquastat HI over 200 F without risking spilling the TP relief valve. You will want to take a look at other measures for improving hot water quantity such as flow restriction or going to an indirect fired water heater.
Question: low limit differential be set for on my electronic oil aquastat L7224?
(Feb 2, 2013) Matt said:
Please see AQUASTAT OPTIMAL LO/DIFF SETTING
Question: Can I set the Low to 140 to keep the furnace from turning off and on so much in warm weather?
(Mar 4, 2013) Question about settings said:
I have an oil furnace to heat the house and part of it to heat my domestic water. It is set at Hi 180 and Low 160. Diff is 25. In warm weather I have a on/off switch on my thermstat. I turn it to off because I don't need heat after April 1st. Can I set the Low to 140 to keep the furnace from turning off and on so much in warm weather? Hopefully saving some energy costs. Thanks for any help you can provide. Cliff
(Mar 4, 2013) Sal said:
When it is working normal, the burner will go on, the circulating pump will kick in,
Then, this is what it does:
What is it doing ?
(Mar 16, 2013) Buddy said:
I found a couple of items that were causing my problem. First, the faucet in our bath tub/shower is the Delta single knob that adjusts both temperature and flow. It is about 45 years old and I have not rebuilt it in the 27 years I have owned the house. I found that even with showering at a good temperature, when the faucet was moved to the full-up high-flow position the temperature would drop. Apparently the internals are worn and there are spots that the water mix changes. Rather than spend a few hundred dollars to try to fix the problem, we no longer try for full flow and that is working just fine. Try different positions of the faucet to see if this might be the problem.
Another possibility is that the shower that gets cold is in another heating zone. My problem was that the upstairs thermostat only started the circulating pump. It would only control the temperature around the LO setting. To make matters worse, the controls were was not wired to cut out the pump when the temperature dropped below the circulator-off LO limit. This problem was made worse since our set-back t-stat would usually turn on for the first time when we were showering and the return water to the boiler of around 63 deg F drastically dropped the boiler temperature which killed heat transfer to the domestic water. Also, the boiler controls were not wired to fire the boiler around the HI setting when the t-stat called for heat. I found that we were heating the upstairs around the LO setting . I rewired the controls and solved the problems but eventually put in and electric water heater to eliminate the frequent minor faucet adjustments needed because of the boiler's moderate temperature swings.
One last thing to check is the tempering valve that mixes heated domestic water with outside cold supply water to maintain a safe domestic hot water temperature. Mine went bad and I replaced only the internals with no soldering required.
(Mar 16, 2013) DanJoeFriedman (mod) said:
Thanks for your comments above.
First, it's never a good idea to set the HI above 200F on the aquastat - you risk dumping the relief valve.
Second, if your aquastat was above 220 your TP valve should have been spilling, so I suspect you have a safety hazard at the boiler - possibly a dangerous one.
Third, ditto my second point above if you actually saw water temperatures above 250F at times - how is this POSSIBLE unless the boiler was under pressure? Water boils at 212 F. WATCH OUT for a BLEVE boiler explosion (search InspectAPedia for BLEVE explosions for details)
Usually when hot water flow rate is poor on a tankless coil system we start by checking for mineral clogging at the tankless coil.
Just go to convenient fixture (I like sinks that use a single lever Delta type faucet handle for this trick) and run cold water at full "on", then switch over to hot at full "on". If hot flow is noticeably less than cold flow then the hot water system is probably mineral clogged, usually right at the tankless coil.
If both hot and cold flow rates are the same, then there is a different problem with system water pressure or hot water delivery piping.
If the system water piping, faucets, etc, is clogging with minerals, rust, crud, setting the temperature up doesn't fix it and actually speeds the clog procedure.
About your "... shower is in another heating zone ..." - I'm a bit confused. The tankless coil is on the heating boiler. IT doesn't know about heating zones.
However it is TRUE that IF we are enjoying a nice hot shower and a heating zone calls for heat, turning on the circulator (or opening the zone valve) for that zone sends a blast of cold water (from the cold radiators or baseboards) back into the boiler, dropping its temp and thus reducing heat for the tankless coil and for your shower). That's why the Aquastat is designed to lock out the circulator at > 20 F below HI.
Search InspectApedia for tankless coil clogging for details on diagnosing and fixing the trouble.
Question: Fleetline boilers: wood/coal, MF110/155 and oil, F-22, with a honeywell aquastat L8124
(Mar 29, 2013) Rau said:
Because a mistake can burn down the house or cause other unsafe conditions, I figure if your heating service technician deliberately disabled something she must have thought it was unsafe. So I can't imagine telling you to just go ahead and hook it back up.
I'd start with a call to the heating service company, speak with the service manager, and tell him your concern.
Question: 8124 aquastat set with bypass
(Mar 31, 2013) Ray said:
The 8124 aquastat was set with the bypass when originally purchased and installed and was a standard procedure for all installations so I don't think it was a safety issue at all. As of now I cannot use the wood/coal boiler at all and that defeats the purpose of having it which is not the original intent. thanks for your comment.
Ray, I'm sorry but I can't say I have a certain and clear picture of what you have installed and thus you must understand the need for caution.
The only bypass wire I know about on the L8124 aquastat is not a "bypass" - at all. There is a wire that can be pulled to disable the LO limit - a feature that is not needed if a boiler is not making use of a tankless coil for domestic hot water. We discuss this and show the blue wire in the article above.
If your indirect fired water heater is properly hooked up, it runs as just another heating zone - you boiler doesn't know it's heating hot water rather than a room in the house.
The LO and DIFF are almost irrelevant to this operation and use, and that may be why your tech disabled that circuit. You don't need it. If you mess with the LO and DIFF and the tech did NOT disable that circuit then you could set the control improperly (e.g. setting the LO too close to HI) and you'll SNAFU the system and lose hot water.
If the LO is connected then turning it up too high locks out the circulator.
Leave the LO and DIFF alone - the indirect water heater runs as a heating zone just like any other heating zone.
Unless your tech did something odd.
Question: DIFF settings
(Feb 3, 2014) emes said:
(Mar 14, 2014) Anonymous said:
As the DIF pertains ONLY to operation of the lo-limit when using a tankless coil, it's not doing anything for you. You can set it down to its lowest setting and if you are not going to disable the LO - which is not needed when there is no tankless coil, you could set that down lowest as well.
Question: cycling hot water temperature drops too low
(Mar 30, 2014) Anonymous said:
I have a oil fired HWBB with an internal hot water coil. The low is at 160, the high is at 180, the diff is at 10. When we shower, the hot water takes a reasonable amount of time to get to the shower, but after 30 secs or so, the water goes to room temperature, stays there for another 30 secs, then gets hot again and stays there. Any ideas?
Interesting; I'm not sure what's happening. On a call for hot water it's the LO and DIFF that are in control. Set the DIFF to its maximum and you should get better performance. Let us know what that does to your system.
(Oct 17, 2014) Anonymous said:
Sounds more like the water in the pipes are in a warm area then a cold area and then finally the hot water gets to your shower.... pipes carry a lot of water and if you have an efficient shower head (recommended always) then it can take some time to get to the hot water from the heater especially if they are the old pipes and your shower is a ways (by pipe not necessarily actual distance to furnace)..You may want to trace the pipes from the shower to the furnace and see where it goes.. through walls which are on the outside of house vs inside, higher lower, etc and even turn the shower on as you hold the pipe at various places to see if what I say is true. Sometimes it is the simple obvious reason in this case just physical having noting to do with furnace, which is why some people are getting instant heaters from Europe and installing them. Speaking of which when i was in Germany the coolest thing I saw was a stainless steal multi tubed towel rack which had the the hot water going through it in the bathroom to dry towels and cloths.. very effective and space saving in small bathrooms with toilet tanks in the wall and use half of what we do per flush and have two flushes, small flush for pee and full tank for solids.... why not in America? Because Americant's have no clue and can't stop being wasteful, can't read the instruction the law the Constitution etc and seemingly can't find or figure out how to use the other brain cell... :-} Let us know what you find .. very interested.
Question: odd thermostat operation
(July 28, 2014) colton said:
I have a dual zone heating system which is oil hotwater with a seperate electric hotwater heater if I adjust the upstairs thermostat to 70 degrees the furnace runs until it reaches that temp if I do the same on the downstairs thermostat the furnace runs and shuts off over and over again and does'nt reach desired temp i had thermostat replaced and four different service people check it's operation and was told that's how it was suppose to work.Any help or suggestions would be great Thank's.
Let's sort out what may be a wiring error by making sure the upstairs heat is OFF and the downstairs thermostat is calling for heat. If the odd behavior continues I'd lookf or a circulator or relay problem.
Question: how do I bypass or disable hot water heating on the boiler
(Oct 19, 2014) Anonymous said:
I just installed a hybrid electric hot water heater and need to know how to bypass or disable the call for Domestic Hot Water for the house and only run the oil boiler for heat. Help
In the More Reading links above the article you want is
Question: wide difference between aquastat settings and boiler temperature gauge readings
12/30/2014 Ryan said:
Great site and info. I noticed that my aquastat and my boiler temp gauge are a good 20 degrees different. My Aquastat's HI might be set to 180 but the boilder temp gauge reads 200 before it shuts off then pending no heat is being called, it might heatsoak all the way to 220. I turned the acquastat HI down to 160 and that seems to make the boiler shut off at 185 and max heat soak i've seen was 205 in this configuration. Do I need a new aquastat or does my compensation method work? Also, is it worth re-greasing the probe well to ensure the aquastat is in good contact with the probe well wall? Any other suggestions?
Another quick question... My boiler has a tankless water heater coil to provide hot water. Recently I had a tech install a 50gal storage tank. The storage tank has no wires going into the the aquastat of the boiler - the storage tank has it's own aquastat that turns a zone circulator on/off. The zone circulator is connected to the in/out of the boiler hot water coil. Do I still need to set my LOW and DIFF on my boiler aquastat (and if so, can you recommend a setting)? What does the storage tank aquastat do in this set-up and how should I set that in conjuction with the boiler LOW/DIFF settings? Currently my hot water measures a max of 155 - 160 degrees coming out of a faucet on full blast hot. Looking for some advice on settings that could save me some $$ in oil yet have little impact on current performance (I.E currently 2 simultaneous 10min showers without issue and plenty of hot left over)
While aquastats and boiler pressure/temperasture gauges are not lab-grade highly-precise instruments, a 20 degree difference may say something is wrong - or might be normal. It depends. Certainly the HI or upper limit setting, say set to 180F should result in a boiler gauge temperature reading close to 180F when the boiler SHUTS OFF at the end of a heat-on cycle. But not always. For example if the burner is firing but the thermostat call for heat is satisfied (the thermostat then turns "OFF", at that point the boiler will stop firing even though it has not reached the cut-off temperature.
But your boiler gauge readings of 20-40 degF above the HI setting suggests something's wrong. It could be a faulty temperature sensor, poor contact between the temperature sensor in its well and the sides of the insertion well (use heat-conductive grease provided by the manufacturer) or a faulty control.
It's possible the trouble is your boiler's gauge - it might be sticking. Because typically if the boiler were truly reaching abnormally high temps, over 200F, the pressure/temperature relief valve should be spilling. I might try installing a new gauge first.
For details on how to set the HI LO DIFF optimally, in More Reading above see the article titled AQUASTAT OPTIMAL LO/DIFF SETTING - and let me know if questions remain.
12/30/2014 Ryan said:
Thanks Joe. At the moment, the aquastat is set to 150HIGH and 120 LOW which is resulting in consistent boiler temps of 180 - 185 HIGH (even when heat soak comes into factor) and 150 - 160 LOW.
I don't notice the boiler temp gauge sticking, it swings very fluidly but I'll read into what it takes to replace the boiler gauge. Since the aquastat is consistently reading LOWER temps then the boiler gauge, i'm guessing (hoping) based on your response the aquastat is not touching the inside of the probe well. I'll take a look and re-insert grease where needed.
On the other subject I posted about: Boiler coil connected to storage tank; Do you have any thoughts there?
Recently I had a tech install a 50gal storage tank. The storage tank has no wires going into the the aquastat of the boiler - the storage tank has it's own aquastat that turns a zone circulator on/off. The zone circulator is connected to the in/out of the boiler hot water coil. Do I still need to set my LOW and DIFF on my boiler aquastat (and if so, can you recommend a setting)? What does the storage tank aquastat do in this set-up and how should I set that in conjuction with the boiler LOW/DIFF settings? Currently my hot water measures a max of 155 - 160 degrees coming out of a faucet on full blast hot. Looking for some advice on settings that could save me some $$ in oil yet have little impact on current performance (I.E currently 2 simultaneous 10min showers without issue and plenty of hot left over) "
Ryan if the gauge seems OK I suspect that the temp sensor on the aquastat is defective or it is not in good thermal contact in the sensor well. Some heating service techs deliberately skipped the manufacturers' instructions to use a thermal grease when installing the sensor, complaining that the grease gets stiff and makes later control replacement difficult. But I believe that the manufacturer knows what's most important in successful installation of their product. Further, the current thermal grease has been improved and doesn't create a stuck-sensor issue any longer.
Ryan if you are using an indirect fired water heater with its own heating zone and controls, you can abandon the tankless coil and disable the appropriate parts of the aquastat - see
AQUASTAT LO & DIFF DISABLED
OR there are other options for using both the indirect water heater AND the tankless coil. For your set-up I don't recommend this, but one can pipe the tankless coil after the outlet from the indirect water heater so that the coil only comes into play as a booster unit if the first heater has run out of hot water. I wouldn't do it. A decent indirect fired water heater is efficient, a good use of the boiler as heat source, and most likely the added support of the tankless coil is not needed.
Reader comment: Ben disagrees and discusses Delta-T
First, running a high boiler temp will increase the heat output of the fin/tube heaters in the room, HOWEVER, this significantly reduces the efficiency of the boil itself since the Delta T at the boiler is less. The goal is to run lower water temps and have longer burn times to reduce heating oil consumption. Outdoor reset is a good example of this. Unless you had a poorly calculated heat loss done when installing your heaters, there shouldn't be a reason to go up to 200*F.
Second, there is no 100% set rule for the low limit. This setting is only for when the thermostat isn't calling for heat (what the boiler will maintain during the summer is a way to think about it). if you have tankless hot water then this controls your hot water temp when not in heat mode. More than likely though this can remain very low since the BTUs required for a shower or a dishwasher is much lower than a whole house heating loop (which is what your boiler is sized for).
Finally Diff setting. This article makes it sound like the diff setting only works off the low switch...which isn't true. The Diff setting sets the upper limit of the high/low settings. say you're running 180/160 with a diff of 10....this would allow 190/170. Now keep in mind, it has nothing to do with the diff under the setpoints. This saying, the boiler will always maintain a 10* below set point. Running a high Diff can increase burn times, but also create variation in water temp....this generally is considered "uncomfortable" by most people (rad temps varying or shower temp not always similar).
So bottom line.....for fuel savings, set the boiler to have the largest Delta T at the BOILER not at the fin/tube.
Ben, we agree and have stated that longer boiler-burner ON times are more efficient ways to run any oil fired heating system.
Our comments AND illustration of how the DIFF works on aquastats is excerpted direclty from the manufacturer's control installation manual data sheets.
About water temperatures and uncomfortable operation, indeed we, and most manufacturers, recoimmend use of an automatic tempering valve at the boiler where a tankless coil is in use, both to avoid scalding burns and to permit higher boiler temperature operation for both greater efficiency and more total hot water supply (longer hot water at the shower before running out).
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