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.

[Click to enlarge any image]

On 2020-02-11 18:50:39.556580 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.

On 2020-02-10 22:28:41.515167 by Bob

Can you use a 30 volt thermocouple when it calls for 24 volt thermocouple?

On 2019-12-19 08:19:49.862335 by Anonymous

William's gas furnace. Thermocoupler had 2 connectors. The replacement does not. It looks like the end is threaded, and a 2 connector block is soldered about 3 inches from the threaded end. I see theres an opening approx the same size. But no wired connectors. I connected the block via jumpers but still can't keep pilot lit.
I'm quickly going from hero to zero here, rep wise.
Thanks for your help.
There is also a limiter, sensor found at top of wall heater.

Buddy

On 2019-02-17 02:33:41.675298 by (mod) -

Walter

Using the on-page search box just above to search this site for FAN WON'T STOP finds FURNACE FAN WONT STOP - at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

please try the diagnostics there and let me know how that works out

On 2019-02-17 01:42:52.490966 by Walter

Heaters been working fine until now when the flame stops the fan keeps running doesn't stop.

On 2019-02-03 16:04:20.521019 by (mod) -

ON systems using a thermocouple and pilot flame the pilot is always on

On 2019-02-03 14:19:51.699591 by Anonymous

On water heater

On 2019-02-03 14:19:02.134640 by Anonymous

Does burner always stay lit

On 2018-10-29 22:08:15.889514 by (mod) -

My guess is that the thermostat 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.

On 2018-10-29 by JemmyStevens

Why is the thermocouple on my furnace burning out every year.

On 2018-01-21 by (mod) - clearing a clogged gas pilot.

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.

On 2018-01-20 by Stevierayray

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,,,Stevierayray

On 2019-02-15 by (mod) - replaced thermocouple but pilot and burner go off

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.

On 2019-02-15 by Karen

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 2019-01-21 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 https://inspectapedia.com/electric/Start_Capacitor_Operation.php 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.

On 2019-01-21 by Joe g

How fix the 2 little fans they make use like wanting work but they don't work once upon a time I used to start them with my finger and they go just give them a spin my self.do I need new fans and or just mother thabks

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

On 2018-12-26 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.

On 2018-12-23 by MJH101

Pilot will stay on,but when you go from ing to the low position the pilot begins to shrink.

On 2018-12-03 1 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.

On 2018-12-02 by Tim J Smith

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 2018-11-27 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

On 2018-11-27 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.

On 2018-11-27 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.

On 2018-11-27 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.

On 2018-11-27 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.

On 2018-11-27 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.

On 2018-11-09 22:41:19.984653 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.

Let me know what you find.

On 2018-11-09 by MikeI

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 2018-10-07 21:27:35.605277 by (mod) -

Thank you for an interesting question.

If you think about it both 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.

On 2018-10-07 16:41:37.923726 by Todd

Isn’t there a difference between gas furnace and gas oven thermocouple ?

On 2018-06-24 12:01:42.678922 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.

On 2018-06-24 02:10:10.523170 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 ?

On 2018-06-18 21:29:35.934800 by (mod) -

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

On 2018-06-18 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.

On 2018-06-18 by Anonymous Reliance 606 water geater Nidek 639x0rt

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 2018-05-30 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.

On 2018-05-30 by Jnolan

Here are some pics. Sorry took so long. My son had to take them and email was not getting thru to me

On 2018-05-25 by (mod) -

You can, if it's easier for you, post a photo to each comment on this page using the "Add Image" button next to the "Comment" button.

On 2018-05-25 by Anonymous

I will send that off this weekend I am away until Saturday thank you so much

On 2018-05-24 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.

On 2018-05-24 by Jnolan

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 2018-04-24 by (mod) -

if the pilot light is remaining lit I don't suspect a thermocouple problem I suspect that you have a gas control or igniter problem

On 2018-04-18 by Bill

Question, Flo-Co furnace, Pilot li pilot pilot light is on , furnace will not ignite , pushed the Thermocouple button nothing happens, any suggestions

On 2018-04-10 by (mod) -

CORRECTION

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

https://inspectapedia.com/plumbing/AO-Smith-Water-Heater-Age-Manuals.php

On 2018-04-10 by (mod) - diagnostic tips: flash codes for Honeywell Gas Valve on a water heater

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.

On 2018-02-18 by (mod) - please don't copy our articles to other websites but hard copy printing is fine

Marge,

Do Not copy our material without permission. Use the page top or bottom CONTACT link to send me information and obta in permission for use in print form only.

On 2018-01-09 by Marge Padgitt

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 2017-12-30 by (mod) -

Lowering flame and "going out" could be an oxygen depletion sensor thinks the system is unsafe. Or your thermocouple sensor is not properly located within the flame.

Also check that the other end of the thermocouple tube is fully screwed in to the gas valve.

On 2017-12-30 y TonyT

I put in a new thermocouple because when the pilot was lit and I turned it went out. Now it worked good for about 15 minutes then acted like it ran out off gas (its not) as the flames got lower and went out.
What would cause that? I also broke the bleeder flat bar off, would that cause it?
TIA

...

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 these

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THERMOCOUPLE TROUBLESHOOTING FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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