How to Use Air Input to Help Drain a Hot Water Tank
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Water heater tank flushout - how to let air into the water tank: Here we explain methods to allow air to flow into the hot water heating tank during a water tank drain procedure. Without this step you may find it difficult to drain down the water heater. We discuss how to use the pressure/temperature relief valve to let air into the water heater to make draining easier, and we describe how to fix a dripping or leaky pressure relief valve or how to replace the pressure/temperature relief valve if necessary.
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How to Let Air Into the Hot Water Tank to Speed-up Water Tank Draining or Flushing Procedures
The articles at this website will answer most questions about diagnosing and curing noisy domestic water heaters and about the procedure to remove mineral deposits, lime, water scale, silicates, sulfates, aluminates, or silt and sand from a water heater tank.
Warnings Before Starting to Work on a Water Heater
Watch out: draining and flushing out a residential water heater is pretty easy and only a few common hand tools (adjustable wrench) are needed. But it's only easy if nothing goes wrong. A stuck or broken control valve or drain valve, or difficulty finding how to drain water out of a basement-located water heater with no nearby floor drain can all present challenges during the drain operation, and there can be a few surprises when you are putting things back together too: a leaky water heater drain valve or leaky water heater relief valve.
See DRAIN a WATER HEATER TANK This article describes dealing with the more common of these water heater tank draining troubles: defective water heater tank drain valve, water heater cold water-in supply valve won't operate.
Our standard water heater drain procedure for flushing out mud, silt and crud as part of regular heater maintenance is at WATER HEATER FLUSH PROCEDURE. See WATER HEATER DEBRIS FLUSH for a detailed photo guide through draining and cleaning out a water heater that had been sending debris into the building water supply piping.
Watch out: Safety Warnings: don't tackle this water heater cleanout project on a Sunday night when you can't call a plumber or buy a replacement part. Water heaters, their heating source (oil or gas burner or electricity or solar hot water), and particularly their relief valves include critical safety components. Do not modify or remove relief valves, chimney connections, draft hoods, etc. as you may create dangerous conditions.
You'll find that just opening the tank drain doesn't do a thing unless there is a way to get air into the water heater tank as water is running out.
- Open a nearby faucet, or as some manufacturers recommend, remove the pressure/temperature relief valve from the water heater tank to let air into the tank and speed the draining process.
Notice that the manufacturers say to remove the relief valve? You could just use that test lever on the valve to open it. Manufacturers don't want you messing with that lever because their experience, and ours, is that on occasion the valve will continue to leak after the lever has been moved. That's what happened to us. Below we describe the problem, what repairs we tried, and what finally worked.
Watch out: you cannot remove the water heater TP relief valve before the water level in the tank has dropped below the mounting point of the valve on the tank top or near the tank top on the side of the unit. Otherwise water will just pour out of the relief valve mounting hole and all over the floor.
Watch out: if the water in the water heater is hot you can be scalded.
Removing the relief valve may also let combustible hydrogen gases formed during deliming (if you use a deliming chemical) vent out of the tank. Soak the relief valve in delimer or in vinegar if its sensor or other components are coated with mineral deposits, or simply replace the valve with a new one (to be extra safe) of the same rating.
When the water heater tank has been fully drained, remove the drain valve and inspect it for clogging or damage - clean or replace the drain valve as needed.
How to Let Air Into the Hot Water Tank to Speed the Tank Draining Process
This article explains using or removing temperature and pressure relief valves on residential water heaters to let air into the hot water tank during draining for cleaning or other purposes. For more details about water heater safety valves see RELIEF VALVES - Water Heaters and for a discussion of temperature and pressure relief valves used as safety devices on heating boilers please see Relief Valves - TP Valves on Boilers.
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It is possible to speed the heater draining and also to ease the flushing procedure if you
open a hot water tap nearby so that you can let air into the heater as water leaves it
Some plumbers open the water heater pressure/temperature relief valve for this air-in purpose - but there is risk that you'll later be unable to get the valve to
shut fully again - debris can clog the valve seat - sometimes we can stop a relief valve from dripping by tapping on the
valve lift rod that protrudes through the valve lift lever
Other plumbers simply remove the relief valve entirely - this is the process recommended by some water heater manufactures such as A.O. Smith. Removing the relief valve makes it easy to inspect this critical safety component itself, and it's easy to clean or replace the safety valve at that time.
When replacing the relief valve use an approved teflon tape or pipe sealant and work neatly and with care so that there will be no leaks at this location.
Safety Warning- a damaged, improperly-selected model, or modified pressure/temperature relief valve is dangerous and could lead to a serious BLEVE explosion
should the water heater later overheat.
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Notice that the manufacturers say to remove the relief valve?
You could just use that test lever on the valve to open it. Manufacturers don't want you messing with that lever because their experience, and ours, is that on occasion the valve will continue to leak after the lever has been moved. That's what happened to us. Below we describe the problem, what repairs we tried, and what finally worked.
Watch out: you cannot remove the water heater TP relief valve before the water level in the tank has dropped below the mounting point of the valve on the tank top or near the tank top on the side of the unit. Otherwise water will just pour out of the relief valve mounting hole and all over the floor.
Watch out: if the water in the water heater is hot you can be scalded.
Removing the relief valve may also let combustible hydrogen gases formed during deliming (if you use a deliming chemical) vent out of the tank. Soak the relief valve in delimer or in vinegar if its sensor or other components are coated with mineral deposits, or simply replace the valve with a new one (to be extra safe) of the same rating.
When the water heater tank has been fully drained, remove the drain valve and inspect it for clogging or damage - clean or replace the drain valve as needed.
The Temperature/Pressure Relief Valve is Leaking on my Water Heater - Now What?
OK so we told you so.
If the TP valve is leaking because the temperature or pressure are too high, it's doing its job.
See RELIEF VALVES - Water Heaters for details about how TP valves work, why they leak, how dangerous leaks or malfunctioning valves may be.
But more likely, even though we told you not to, you tried messing with the test lever, you left it in the "open" position as a quick easy way to let air into the water heater tank. To be honest, we do this too. But we never ever touch that lever unless we are prepared to either leave the water heater shut off entirely OR we are prepared to go buy and install a new TP valve.
Here are some things to try if the TP valve is just dripping:
Tap gently on the rod that protrudes through the test lever and that would be pulled (against an internal spring) when you lift the lever. Sometimes a gentle tap will seat the valve and it'll stop leaking.
Watch out: Tap GENTLY. If you bang on it and damage the valve or seat or internal washer, the leak will get worse.
Lift the valve and flush the valve seat. That's what we tried recently when our TP valve was leaking after draining the water heater discussed at WATER HEATER DEBRIS FLUSH. That heater tank had a lot of floating debris particles and we had the fantasy that we could flush the valve seat and it'd stop leaking. It didn't work.
Watch out: The risk too is that if the internal TP valve washer is in poor shape, you may blow out the washer or part of it when you open and flush the valve, making the leak worse. We lifted, flushed, then tried the tapping trick again. It didn't work. The water heater was cold so we knew this wasn't an overheat or overpressure problem.
Put a bucked under the valve extension tube so we don't flood the floor.
Watch out: But do NOT accept this as a remedy. If you leave the valve leaking it may eventually stop leaking due to build up of mineral deposits from the hot water passing by. Then you have no working TP valve and there is a risk of water heater explosion.
Replace the TP valve with a new unit. That's what we had to do in the system discussed at WATER HEATER DEBRIS FLUSH. The valve dripped on the floor over the weekend until the owner bought a replacement TP valve.
Here are Detailed Steps in How We Replaced a Water Heater Temperature/Pressure Relief Valve
- Cool down the water heater by turning off the burner and running "hot water" in the home until it came out cool
- Turn off water supply to the water heater.
- Drain enough water out of the water heater so that water level is just below the level of the TP valve where it mounts on the tank. If you're not sure, and since you're going to replace this valve anyway, you might try opening it with the test lever - if no water comes out, maybe the water level is low enough - provided the valve opens at all.
- Remove the TP valve extension tube - set it aside for re-use
- Remove the TP valve by unscrewing it from the water heater - counter-clockwise is "unscrewing" - it may take a big wrench if the valve is stuck or glued in place.
Watch out: for breaking off a valve or stripping threads in the mounting opening on the water tank - that could lead to complete water heater replacement.
- Compare the data tags on old and new Temperature Pressure relief valve to be sure we've bought the right item - the valve must have adequate BTU, temperature response, and pressure dumping capacity or the water heater will be unsafe.
- Prepare the new TP valve threads with teflon tape or teflon pipe dope.
- Screw in the new TP valve carefully, ending with the valve pointing downwards if it's mounted on the side of the water tank.
Watch out: don't over-tighten the valve - you may end up with the valve fully tight but not pointing down. Just backing it off might lead to a leak. If you make this mistake remove the valve, re-wrap with teflon tape and start over. We always use the smallest wrench that will work when installing threaded parts in order to avoid damaging something.
- Restore the TP valve extension tube
- Refill the water heater
- Turn the water heater back on.
Watch out: do not turn on an electric water heater with no water in the tank - it'll be destroyed.
- Check for leaks - don't mistake a few drops of water left in the extension tube for a leak - water may have been in the tube from the prior leaky valve.
- Check again in 24 hours for leaks at the end of the extension tube.
That's it.
This article series continues at WATER HEATER SCALE - De-Liming Procedure or at WATER HEATER DEBRIS FLUSH depending on which procedure you're attempting.
If you \were dealing with water heater scale and lime, after flushing out the water heater tank, the second step in curing water heater noise or insufficient hot water is to remove scale or lime from the water heater tank. If the unit is an electric water heater, you'll also need to remove scale from the electric water heater elements. See WATER HEATER SCALE - De-Liming Procedure for the full article on the detailed procedure for removing lime and water heater scale.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
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- Thanks to researcher Robyn Goldstein, Rush Manager, Information Express, 650-812-3585, email: service@ieonline.com,for researching the Purdue bulletin No. 74 original citation 03/2010
. Information Express supplies "... institutional document delivery needs - A full service company specializing in the fast, accurate and competitively priced delivery of published articles for all industries"
- Pounds of lime deposited vs. temperature and hot water usage: see Purdue Bulletin #74 (also provided by A.O. Smith in the article below). Purdue's chart shows the number of pounds of lime deposited per year as a function of the water usage in gallons per day, with an assumed 10 grains of water hardness.
- "When, Why, and How to Remove Water Scale from Tank Type Glass-Lined Water Heaters (for non glass-lined tanks, consult water heater manufacturer)" PDF provided by A.O. Smith Water Products Company - hotwater.com/lit/training/4800r9.pdf 800-433-2545 - 01/07/2009.
- A.O. Smith's Form No. 4800 Rev. 8 Why? When? & How? /UN•LIME Specific Deliming Instructions for use with Up-N-Down Transfer
Kit for Tank Type Heaters. (Normally supplied in UN-LIME shipping cartons),
Supersedes Form Nos. 4800 Rev. 7 and 4813-100.
- A.O. Smith's Form No. 4778* All about Deliming Coil-Type/Tube-Type Commercial Water Heaters and Hydronic Boilers *Normally supplied when ordering Part No. 4930 Motorized Deliming Pump Kit
- Rheem Electric Water Heater "Owners Guide and Installation Instructions", (Australian models) rheem.com.au/images/pdf/owners_dom-elec_121996C_0707.pdf
- "Scale formation in water heaters and methods of prevention", Krappe,
Justus Maximilian, Engineering experiment station. Gas engineering
bulletin; no. 6; Research series; no. 74; On cover: Engineering
bulletin, Purdue university. Vol. xxiv, no.
3a. June, 1940 (Layfayette Indiana) commonly referred to in some references as "Purdue University Bulletin No. 74" - thanks to researcher Robyn Goldstein for the full citation. LCCN: 40028844 & OCLC: 1038544 - Water analysis, water softening, hot-water supply. 27pages. You can obtain this document through your local library.
(full copy file at InspectAPedia 3/31/2010)
Purdue B074 can be hard to locate online.
Also Bradford White Corporation (a manufacturer of water heaters) has published excerpts from that document, available at Purdue_B074_BradfordW.pdf
- Super Iron Out, MSDS Material Data Safety Sheet rust and stain remover; the manufacturer indicates this product can be used to clean rust sediment from water softeners. Summit Brands. See Iron Removal from Water Softener
- Lime Out / Lime Out Extra, lime remover MSDS, produced by Summit Brands, 7201 Engle Road, Fort Wayne, Indiana 46804–222, Tel: 1–888–476–6688, Email: info@summitbrands.com Email
See WATER HEATER SCALE - De-Liming Procedure
- Other sources of information on calculating the rate of lime deposition from hard and hot water:
- Wilkes University Center for Environmental Quality Environmental Engineering and Earth Sciences Hardwater, Water Hardness "Hard Water Hardness Calcium Magnesium Water Corrosion Mineral Scale" http://www.water-research.net/hardness.htm
- Chemical Engineering, Joseph D. Hagerty Editor, McGraw-Hill, 1989,
ISBN 0685270831, 9780685270837
"To calculate the amount of material that will be deposited in 1000 gal. of water per day, take the number of grains per gallon of each as shown by the ..." also difficult to obtain except as a used copy.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
- ...
