Recent Thermocouple diagnostic FAQs for heating appliances - set #2.

We include typical LED flash codes for a Honeywell gas control valve used on many water heaters.

This article series describes thermocouples, safety devices used on gas fired heating equipment.

Q&A on Thermocouples & Thermopiles in Gas Fired Heating Equipment

These questions & answers about diagnosing, fixing or replacing thermocouples on building heating equipment were posted originally

at THERMOCOUPLE REPAIR / REPLACEMENT. Be sure to review the troubleshooting and repair advice given there.

Illustrated here: a typical gas fireplace thermocouple assembly showing its principal components. This particular unit is a model 70K0 Thermocouple.

OK to use a 30mV Thermocouple to replace a 24mV unit?

Can you use a 30 volt thermocouple when it calls for 24 volt thermocouple? On 2020-02-10 by Bob

Reply by (mod) -

Bob

I think you mean millivolt, not volts, right? I 30 millivolt thermocouple is pretty much the current industry standard and should be fine.

Does a water heater burner always stay on?

Does burner always stay lit - it's on a water heater? On 2019-02-03 by Anonymous

by (mod) - No but a constant pilot will stay on

On a water heater it is NOT normal for the acutal burner flame to remain on constantly.

Watch out: if that's happening on your water heater, for safety (scalding burns or a building fire) turn it OFF and call for repair.

Now maybe you're asking about the pilot light, not the full burner flame.

On systems using a thermocouple and pilot flame, the pilot is always on.

Other gas appliances may use intermittent ignition or an igniter system that turns on at the call for start-up at the burner.

Why does my furnace thermocouple burn out every year?

Why is the thermocouple on my furnace burning out every year. On 2018-10-29 by JemmyStevens

by (mod) -

My guess is that the thermocouple is not installed correctly, perhaps not positioned correctly in the flame. Or it may be the wrong part number for your heating Appliance. The other possibility is that the thermocouple may be getting damaged during installation.

Pilot light shrinks when the burner goes from ignition to "low"

Pilot will stay on, but when you go from ing to the low position the pilot begins to shrink. On 2018-12-23 by MJH101

by (mod) - cleaning the orifice for the pilot and the pilot assembly

I would start by inspecting and cleaning the orifice for the pilot and the pilot assembly. I've occasionally found spiders and insect nests inside the pilot.

If the problem continues there could be a regulator or pressure issue as well.

 

How to safely clear a clogged pilot flame on a gas burner?

I just want to post this so it might help others with the same problem that I ran into today with my Empire NG SR-18T REVISION(3) wall mounted heater

.I have had this heater for 15 years and it has been and still is a good one. I clean it out,vacuum it with my shop vac,then reverse my vac so it blows air I then blow air through the little hole in the Pilot Tube (the tube that ignites where the blue flame lights) in other words the pilot light.

Usually I just use a straw,put it flat against the little hole and blow air in there and if any blockage,it will usually fly out when I blow through the straw,dust,lint,spider webs,etc,2 or 3 times a year.

Ok,yesterday(1-18-2018) I had the heater on and heard the loud audible click that you hear when the pilot light goes off and it shuts the gas valve off(safety feature)!

Ok,then I turned the Temp Control Knob off and waited about 5 minutes or so and turned the knob to pilot,pushed the igniter button a few times and the pilot lit but only was about a 1/2 inch long,where normally it's a 2-3 inch pilot flame,and when I released the pilot knob the pilot flame would go out,every time?

Now I'm scratching my head? i then looked in the owners manual again and it states to do what I already have done and

QUOTE>"WARNING">Never use needles, wires, or similar cylindrical objects to clean the pilot to avoid damaging the calibrated ruby that controls the gas flow.

Well.I followed the directions,although I wanted to run something down in the pilot tube!

I read that manual so many times it's given me a BAD headache,now I'm fixing to order an Empire R6306 Pilot Assembly (NAT) Includes R-6309 & R-6310,around $34.00,not bad for 15 years,

BUT? I told/showed my son and he has a friend who is a Heating and Air Tech.

So,today (1-19-2018) I still had it taken apart,Tech comes by,takes my bread tie off my bread bag,pulls the nylon covering off the little wire(bread tie),loosens the nut on the pilot tube,moves gas line over gently (the one coming from the GAS VALVE) , sticks that little wire in the pilot tube, ran it around in there a few times and some love fell out of the pilot tube, vacuumed it up,

turned the gas cutoff under the heater back on,turned knob to pilot,pushed the igniter one time,BAM,fired right up first push on igniter with a stronger,longer(3 inch pilot light) blue flame,better than when it was new,and working like new again,also plugged my blower back up(Optional Blower) that I had unplugged!

Tech was here less than 5 minutes, NO CHARGE!!! Hope this helps others with the same or similar problem.... Good Day to all, On 2018-01-20 by Stevierayray

Reply by (mod) -

Stevie

Thank you for the helpful comment about clearing a clogged gas pilot.

Indeed I have often found clogs caused by insects who move in to small openings in equipment, especially if the pilot or burner are left off for a time.

I replaced thermocouple but pilot and burner go off

Replaced the thermocouple on my elderly Williams dual wall heater a couple of years ago.

Lately it has started acting up. I don't have any trouble lighting the pilot. The flame is blue and looks a nice size. Then the heater works cycling on and off as you would expect. At some point, the burner goes off and the pilot light is also out and I have to light it again.

Sometimes this takes 30 minutes, sometime several hours. I have used canned air to clean and pushed and pulled everything. Hope someone has some wisdom for me. Thank you. On 2019-02-15 by Karen

Reply by (mod) -

Check the thermocouple connection at the gas valve

Watch out: also check for lack of combustion air - your heater may include an oxygen sensor that shuts down the system if there is insufficient combustion air - as that risks fatal CO poisoning or poisoning from lack of oxygen in the room.

How do I fix the little fans on my greenhouse heater ?

How do I fix the 2 little fans on my heater? I used to start them with my finger and they would go if I'd just give them a spin myself.

Do I need new fans and or just something else? On 2019-01-21 by Joe g

Hi I have a heater in a extra room which I use for green house room piled light went off a couple times .I turned it back on with know problem but it won't let me turn the knob to the on position get stuck on off .but was turning before now it goes from piled to off thanks

by (mod) - trouble with fans in a gas fired greenhouse heater

Joe

Before replacing fans that will start and run if given a spin, check to see if the fan motor uses a start/run capacitor and if so, replace those.

See details at HOW a STARTING CAPACITOR WORKS

Note that what you describe - a fan problem - could be INDIRECTLY related to a gas burner or pilot or igniter problem in that if the burner doesn't run, neither would we expect the heater's blower fan to run.

 

Diagnostic tips: flash codes for Honeywell Gas Valve on a water heater

Here are some additional diagnostic tips for gas fired water heaters using the Honeywell gas valve shown below: this gas valve, used on many gas fired water heaters (AO Smith, Rheem, State, Whirlpool) provides a diagnotic LED whose flashes mean the following:

1 intermittent flash: the heater is operating normally

2 flashes followed by a pause, then two flashes: inadequate (low) voltage at the thermopile. If wiring is intact and properly connected you need to replace the pilot assembly, including the thermopile

4 flashes: excessive or unsafe water temperature - shut off the heater and call for repair. Replacethe gas valve (most-common repair) as the problem is most-likley that the gas valve is not properly sensing water temperature

5 flashes: sensor failure - the gas control valve needs replacement since the temperature sensor is integeral with the valve

7 flashes: the gas control valve has failed. Replace the gas control valve.

8 flashes: electrical power has been lost. Re-set the control valve by turning the dial to "off". Wait a minute or two. Turn the dial back on to a mid-range temperature. If the burner ignites and the heater works then you're ok; else the valve may need replacement.

Our links to A.O. Smith water heater repair manuals and other information are found at

AO SMITH WATER HEATER AGE, Manuals , ERROR CODES 

Ventless LP Gas Heater Won't Stay Lit

I have a LP ventless heater that fits on top of a LP tank. It has a red push botton on it that you push in and light it, but when I let go of it the heater goes out. What is wrong with it? On 2018-12-02 by Tim J Smith

Reply by (mod) -

First check the position of the control dial to see that it has been turned to the light or ignite position.

Then if you get a flame but the pilot goes out when you let go of the button I suspect that the thermocouple has failed.

In this article series you will find articles on thermocouple troubleshooting and repair.

Our pilot light ignites but the burner won't come on at our heater

The heater was working good then when it went off it wouldn't come back on the pilot is lite and the blower comes on but the burner will not come on. On 2018-11-27 by Charles Hiatt

by (mod) - safety warning about flue gas spill switch

Charles:

If the pilot light stays on then we think the gas supply is working.

But some water heater safety devices such as a flue gas spill switch on some models will turn off the water heater and require a manual reset.

Look for a flue gas spill switch..

Watch out: if the flue gas spill switch shut off a gas fueled appliance you should leave it off until your service tech or chimney sweep has confirmed that the heater is venting safely.

Otherwise you risk fatal (death) from carbon monoxide poisoning.

by Charles Hiatt

The heater was working good then when it went off it wouldn't come back on the pilot is lite and the blower comes on but the burner will not come on.

Reply by (mod) -

Charles:

If the pilot light stays on then we think the gas supply is working.

But some water heater safety devices such as a flue gas spill switch on some models will turn off the water heater and require a manual reset.

Look for a flue gas spill switch..

Watch out: if the flue gas spill switch shut off a gas fueled appliance you should leave it off until your service tech or chimney sweep has confirmed that the heater is venting safely.

Otherwise you risk fatal (death) from carbon monoxide poisoning.

by Charles Hiatt

The pilot is working the blower is working this is a ceiling mounted garage furnace fired by natural gas I think it does have a vent it was working good till it reached the set temp.when it shut off it would not come back on I thought it could be the thermocupling but some said it doesn't sound like gas valve problem does anyone know what it might be.

Reply by (mod) -

The added details help a bit but of course it's always incomplete to pretend diagnosis of a heating system by e-text: all we can see is what you have noted and reported.

I would look for

- a loose or corroded electrical connection including at the fan limit control switch

- a bad fan limit control

After reinstalling my gas pilot light and thermocouple the pilot goes off when I turn the control to ON

I just finished reinstalling my pilot and thermocouple. The pilot would not lit and i had to clean it. After reinstalling to make sure they were aligned correctly, the pilot lit and remained on after holding the button down for a few seconds.

The pilot will stay lit as long as you dont switch to ON. If you rotate the knob to ON, it immeadiately goes out. I checked the thermocouple voltage at the valve body and it is 582 milliamperes. Suggestions? On 2018-11-09 by MikeI

Reply by (mod) -

MIke

Sometimes I find the trouble is I haven't fully seated the other end of the thermocouple -at the gas valve, or worse, it was cross-threaded and created an ugly mess requiring complete valve replacement.

So check that connection with care.

I've also seen this problem when the thermocouple was failing or when the end that secures to the gas valve is not fully seated. Sometimes just tightening that nut fixes the problem.

Watch out: it may be threaded backwards from standard.

Let me know what you find.

What's the difference between a thermocouple for a gas furnace and for a gas oven?

Isn’t there a difference between gas furnace and gas oven thermocouple ? On 2018-10-07 by Todd

by (mod) -

Thank you for an interesting question.

If you think about it both flame sensing thermocouples for both appliances are doing about the same job, that is responding to the presence of a flame produced by the same fuel so you would expect them to differ principally in the fittings.

Watch out: don't confuse the oven temperature sensor with the gas flame thermocouple.

Reliance 606 water geater Nidek 639x0rt pilot shuts off after the unit gets hot

The name of the heater is

Reliance 606 it is 30 gallons serial no.A04158574

and model no is 630x0rt.

Some pics attached 8t will still heat up some for about half hour then pilot shuts off On 2018-06-18 by Anonymous

by (mod) - Thermocouple Thermpile replacement procedure for a Reliance water heater

Anon

at Reliance's list of manuals http://www.reliancewaterheaters.com/resources/instruction-manuals the Model No. you report does not appear.

Here is a typical Reliance 30 gallon gas water heater manual

http://www.reliancewaterheaters.com/media/72552/100264285-RELIANCE-N3-GAS-ULN.pdf

You will see that the manual absolutely does include instructions for replacing the thermocouple.

just use the "add image" button to add one photo per comment.

I think your model is probably a 30 gallon 630 SHORT gas water heater from reliance, such as the model RELIANCE 30 GALLON FVIR GAS WATER HEATER for Manufactured (Mobile) Homes 6 30 NOMT [PDF] - 30 Gallon Mobile Home Natural Gas/Propane Water Heater - 6 Year Warranty

availble from the reliance link I gave before or from

RELIANCE WATER HEATER AGE & MANUALS inspectapedia.com/plumbing/Reliance-Water-Heater-Age-Manuals.php

by (mod) -

Ballpark is probably an hour. I replace thermocouple is but not on this particular heater and it looks as if there's a bit more disassembly required.

by Anonymous

Thank you it sounded suspicious to me. I will see if another plumber will replace it. Do you know how long it should reasonable take ?

Tech says it'll cost $1,300 to replace a bad thermocouple because myt heater is a sealed unit

I have been told my thermocouple is bad and it is a sealed unit I have to replace hot water heater for 1300 dollars crazy.

Why can't it be replaced. I mean the thermal coupling On 2018-05-24 by Jnolan

Reply by (mod) -

That sounds weird to me too. Give me a photograph of your water heater and of the brand markings and of the data tag that shows the model and serial number and let me do some research. It ought to be repairable.

There must be something we're missing.

Reply by (mod) -

Thanks JN

It would be helpful to see the brand of the water heater - usually a marking or logo elsewhere on the heater - and in a sharper photo of the data tag its model and serial no. I couldn't quite make that out.

The thermocouple connects to the gas valve on the water heater.

I can see just the top of the valve.

Show me the whole heater and then the whole bottom of the heater from just above the gas valve - I want to see the presence/absence of an access opening.

OK to reprint this article in the Midwest Chimney Safety Council News Magazine?

I would like to reprint this article in the Midwest Chimney Safety Council News Magazine. Please contact me at margepadgittmcsc@gmail.com or 816-461-3665. Thank you!On 2018-01-09 by Marge Padgitt

by (mod) - please don't copy our articles to other websites but hard copy printing is fine

Marge,

Generally we'll give permission to reproduce any InspectApedia material in PRINTED HARD COPY form only.

Let us know if you want to do that.

Please don't reproduce our material online or electronically.

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Continue reading at THERMOCOUPLE REPAIR / REPLACEMENT - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see THERMOCOUPLE TROUBLESHOOTING FAQs-2 - more-recent questions and answers about thermocouples and thermopiles

Or see these

Recommended Articles

• GAS BURNER FLAME & NOISE DEFECTS
• GAS BURNER SOOT CAUSE & CURE
• GAS BURNER PILOT LIGHT PROCEDURE
• GAS REGULATORS & APPLIANCE / HEATER CONTROLS
• GAS FIRED HEATING BOILER PROBLEMS
• GAS FIRED WATER HEATERS
• GAS IGNITER DIAGNOSIS & REPAIR
• THERMISTORS in ROOM THERMOSTATS
• THERMOCOUPLE REPAIR / REPLACEMENT
• THERMOCOUPLE SAFETY
• THERMOCOUPLE LOCATION
• THERMOPILE vs THERMOCOUPLE
• THERMOCOUPLE INSTALLATION
• THERMOCOUPLE DIAGNOSIS
• THERMOCOUPLE TYPES
• ZONE VALVES, HEATING

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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