How to Diagnose & Fix Cold Radiators, Baseboards & Convectors - hot water heat
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COLD HOT WATER BASEBOARD or RADIATOR - How to fix a cold radiator or baseboard - No Heat? What to check first on a hot water (hydronic) heating system.
- How to bleed air out of a radiator
- How to identify, inspect, diagnose, and repair problems with hot water or steam radiators, baseboards, or heating convectors
- How to inspect, diagnose, and repair problems with steam radiators
- If your radiator or baseboard is cold and the heating system is "on" - here we diagnose the problem
- Where leaks occur on hot water and steam radiators, convectors, and baseboards
- Guide to unusual radiators, baseboards, and heating convectors in buildings
COLD STEAM HEAT RADIATORS - separate article
RADIATOR VALVES & HEAT CONTROLS - separate article
ZONE VALVES - separate article
Questions & Answers about troubleshooting cold radiators, convectors, baseboards on hot water heating systems
References

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Troubleshoot cold radiators, baseboards, convectors in hot water heating systems: this article describes the diagnosis & repair of cold "hot water" heating baseboards, convectors, radiators, or "hot water" radiators. We provide articles that help in diagnosing and repairing no-heat problems with each types of hot water or steam or fan convector heat delivery systems.

What to Check First if your Radiator, Baseboard, or Convector is Not Getting Hot

If your heating system uses steam radiators or steam convectors see COLD STEAM HEAT RADIATORS for help in diagnosing and fixing steam radiators that won't get hot.

This website answers most questions about all types of heating systems and gives important inspection, safety, and repair advice. If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES. If your heating system is not working properly, see NO HEAT - BOILER. Our page top heating system illustration is provided compliments of Carson Dunlop Associates.

If none of your heating radiators, baseboards, etc. are getting hot, start your diagnosis of the problem at NO HEAT - BOILER / FURNACE DIAGNOSIS. It may be that your boiler is simply not running, has lost power, is switched off, or that the thermostat is not calling for heat.

If you have heat in some areas but not others we discuss diagnosing baseboard heat problems below, followed by a discussion of radiators and convector unit problems for both hot water and steam heat.

Guide to Diagnosing & Fixing Cold Heating Baseboards

Cold Heating Baseboard Diagnostic Guide: how to diagnose a heating baseboard section, loop, zone, or room that is not receiving heat.

Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat. (See THERMOSTATS.)

Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally. A hot water heating boiler may not turn on immediately when you turn up the room thermostat: if the water temperature in the boiler is already above the aquastat's cut-in temperature the circulators will send hot water to the radiator and the boiler will turn on later when its temperature is dropped by returning water from the cooler radiators in the building.

If your heat is provided by baseboards there will not normally be individual shutoff valves at those devices, but if your system uses one circulator and provides multiple heating zones (and thermostats) there will be zone control valves (usually near the boiler) that are opened or closed by the room thermostat(s).

Air-Bound Baseboard Heating Zone Diagnosis

Once your thermostat is calling for heat and the heating boiler has been running for ten minutes or more, just feel the baseboard. Don't cut your fingers on the fins, and don't bend them if you can help it.

If some sections of baseboard are not easy to access that's ok - you can simply feel the start and the end of a section of baseboard to determine where the loop of heat piping is hot and where along the system the baseboard piping first feels cold.

Our photo (left) shows an older finned copper tubing baseboard system with the end-cover removed - it's easy to just touch the copper pipe to feel its temperature - hot or cold, that's all we need to know.

If just some sections of an individual zone or loop of heating baseboard are not getting hot, feel along the piping entering and leaving each section of baseboard in each room to find which sections are hot and which are cold - this is a first diagnostic step in determining what's wrong.

If your heat is distributed entirely through one zone (one thermostat, one loop of heating piping & baseboards) and if part of that loop is warm (usually just the beginning portion of the loop), then there is a good chance that your heating zone or loop is air-bound.

We provide detailed, step by step procedures for diagnosing and curing an air-bound hot water heating system, beginning at AIRBOUND HEAT SYSTEM REPAIRS. Also see heating baseboard air bleed valves discussed at Air Bleeder Valves for more details. Since on many hot water heating systems a key air bleeding or air vent point is at the air scoop or air separator closer to the boiler, see Air Scoops Purgers Separators.

Thermostat, Zone Valve, or Circulator Pump No-heat Diagnosis for Baseboard Heat

If your heating system is divided into multiple zones of baseboards or a mix of baseboards and radiators: If the heating boiler is running and some baseboard sections or rooms are hot but others are not, first check to see if your heating system uses multiple thermostats and multiple heating zones.

It may be that the thermostat controlling the "cold" rooms is not calling for heat or is not working. See THERMOSTATS.

It could also be that the circulator (see Circulator Pumps & Relays) or zone valve (see Zone Valves) controlling flow of hot water to that heating zone is not working.

If your heating baseboard is installed over a carpeted floor, be sure that the carpeting has not blocked the air inflow space under the bottom edge of the metal baseboard cover. Blocking this air intake will drastically reduce the heat output from your heating baseboards, thus increasing your heating bill.

Guide to Diagnosing Cold Hydronic (hot water) Radiators in buildings

If your heat is provided by individual hot water radiators or convector units, usually there is a control valve at each radiator or convector. Make sure that the control valve at the heating radiator is "open" or "on". In the "cold radiator" diagnosis article below we include links to additional detailed articles that will help you correct a problem with heating baseboards or radiators that are not working:

Check the radiator control valve: If a radiator is not getting hot: (steam or hot water) first see if the valve that controls it has been turned off. Try turning the valve counter-clockwise to see if it will open. See details at RADIATOR VALVES & HEAT CONTROLS.

In our photo (left), the heating convector control valve was found at floor-level under the heating convector. The "open" and "close" directions for this "radiator valve" were nicely marked by the manufacturer (click to enlarge the photo).

If the radiator valve does not turn in that direction, try turning it in the other direction (clockwise or "closed") to see if the radiator valve is stuck. You may also find the same control valve at heating convectors (but not usually at heating baseboards).

While people sometimes turn off radiators in an un-used portion of a building we usually find that they have been left "on" - in fact turning off a hot radiator in some building areas could lead to its freezing and cracking. Steam radiators, on the other hand, can usually be turned-off with impunity since steam radiators do not normally contain water in its liquid form. [That's true at least so long as condensate has not become trapped inside of the steam radiator.]

Watch out: don't use excessive force to try to turn a "stuck" radiator valve. First, you may be trying to open a valve that is already in its fully-open position. Second, the valve may actually be jammed. Excessive force can break the valve or even cause a leak. If the valve won't turn at all counter-clockwise towards "open", try turning it the other way - clockwise, towards "closed". If the valve now turns you'll know it was already in its open position.

Thermostatically controlled radiator valves:

If you have to replace the control valve on a hot water or steam radiator or convector unit, consider installing a new valve that incorporates a thermostat as well.

This (more expensive) radiator control valve lets you treat each individual radiator as a "heating zone".

As long as the thermostat is calling for heat, each radiator can be regulated automatically.

If only some of your hot water radiators, hot water heating convector units, or hot water baseboard heating sections are not getting hot and the radiator valve is open, see AIRBOUND HEAT SYSTEM REPAIRS.

In our photo at left you can see not only the radiator control valve, but lots more information: we can conclude that this is a hot water heating system, not a steam heat system because first, the valve is mounted at the top of the radiator (water, not steam - steam enters at a radiator bottom but sometimes so does not water; the reverse is never true).

Second, the radiator control valve includes an air bleeder - that nut on the side of the valve body. In looking for an air bleeder in our article at Bleeder Valves it's easy to miss this particular air bleeding device.

Watch out: even if the radiator valve appears to be "open" - that is, turned fully counter-clockwise, if the valve is broken internally you may be just turning the knob but the valve may be staying closed inside.

Usually while turning a radiator valve to from "closed" to "open" position, if you look closely at the valve stem - the metal rod or shaft extending below the knob you are holding, and extending into the body of the valve itself - you'll see that as you "open" the valve the stem gets "longer" and often a less-oxidized, shiner part of the valve will become exposed as it moves upwards from having been inside the valve body.

That's a great way to convince yourself that yes, the valve is probably opening internally too, you're not just turning the knob. If the valve body has broken loose from the valve stem, that's an internal problem you can't see, but turning the radiator valve knob, even if it rotates, will not open a broken, stuck, frozen valve.

On a heating convector unit there is usually an individual valve that lets the unit be turned down or off - but as our photo (left) shows, the valve can be a little harder to spot.

Unlike a radiator valve, a heating convector control valve may be hidden by the convector's steel cover, or it may be little and hard to recognize as we show here.

This valve, if it's not jammed by corrosion, is operated by a screw driver; it may be possible to get this valve working by gently loosening the lock-nut and then turning the control screw with a flat-bladed screwdriver.

Do not take apart this valve while the heating system is on and hot - you risk getting sprayed with hot water or you may start a leak that's hard to stop without making a mess and having to shut down the whole heating system.

How to Bleed Radiators of Trapped Air

If just some of your hot water radiators are not getting hot you may just need to bleed or remove air from the "cold" hot water radiator, baseboard, or heating convector unit, see Air Bleeder Valves. Carson Dunlop's sketch (left) shows a common location for the air bleed valve on a cast iron radiator.

The advice to leave this valve alone is intended for home inspectors who don't want to risk spilling water on someone's floor or opening a valve to find that they can't close it again.

See Air Bleeder Valves for details about how to get an individual cold radiator working again if it's air bound, and see AIRBOUND HEAT SYSTEM REPAIRS if the cold radiator, convector, or baseboard problem seems to affect all of the heating radiation devices on all or part of an individual heating piping loop or zone.

Also see heating baseboard air bleed valves discussed at Air Bleeder Valves for more details. Since on many hot water heating systems a key air bleeding or air vent point is at the air scoop or air separator closer to the boiler, see Air Scoops Purgers Separators.

Hot water heating boilers, their inspection, diagnosis, and repair are discussed beginning at BOILERS, HEATING.

Guide to Fixing Cold Steam Radiators: Steam Vents & Radiator Slope

If your heating system uses steam radiators or steam convectors see COLD STEAM HEAT RADIATORS for help in diagnosing and fixing steam radiators that won't get hot. Excerpts from that article are found below.

Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat.

Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally. A steam boiler will usually turn on right away in response to the thermostat being turned up or on a call for heat.

Make sure that the control valve at the heating radiator is "open" or "on" as we describe just below. Details are at RADIATOR VALVES & HEAT CONTROLS.

Radiator control valve (C) Daniel Friedman

First check the radiator valve. At Guide to Diagnosing Cold Radiators in buildings we illustrated different types of heating radiator control valves and explained their operation.

It's standard to ask first "is the radiator valve turned on or "open" (fully counter-clockwise)?

But other problems can cause a steam heat radiator to stay cold when you want heat. Here is diagnostic and repair advice.

Steam vent on a radiator (C) Daniel Friedman

If some of your steam heat radiators are not getting hot, the steam vent may not be working.

If a steam radiator valve is open but the radiator is still cold, the steam vent may not be working. Our photo (above right) shows a typical steam radiator vent.

When steam is first rising in the heating system, the steam heating radiator will be cool as will be the steam vent. The vent opens, allowing rising steam to enter the radiator by pushing air out through the vent.

When the steam radiator and steam vent are warm or hot, the vent closes. If a steam vent stops working, rising steam cannot enter the radiator and it will be slow to heat or may not heat at all.

See STEAM VENTS and also STEAM HEATING SYSTEMS for details.

Steam radiator sloped the wrong way - steam condensate blockage

As our Carson Dunlop sketch shows (above, left), steam radiators can be sensitive to exactly how they are installed and pitched or sloped.

You'll want to learn if your steam heating system is a "one pipe" or a "two pipe" design, but in either case, if the steam supply or condensate return piping have been moved or settled so as to have lost the proper slope, correcting those conditions may be needed.

That's because condensate, produced by cooling steam in the radiator, has to be able to drain back out of the radiator.

A steam radiator that is sloped the wrong way, perhaps due to building floor settlement or a change made by an inexperienced remodeler, will become partly or even completely blocked by accumulated condensate, leading to loss of heat.

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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:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- 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.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
  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.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

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.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. 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.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

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.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Links to our list of additional information on heating system inspection, repair, maintenance
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