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Jerry, Plumber
Category: Plumbing
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Experience:  over 20 years residential plumbing experience.
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Ok - I need gas fireplace expert. I have a Heatilator model

Resolved Question:

Ok - I need gas fireplace expert. I have a Heatilator model GNDC36 NAT. It is about ten years old and starting last year it started to run intermittantly. I would turn on wall switch and then after a few minutes it shut off - then sometimes restart by itself - then shut off for good - all the while the pilot was always lit.

So yesterday I finally had some cycles and did some google research. It was suggested that a thorough cleaning might do the trick. So I shut off gas and thoroughly clean regulator; pilot and coonectors as well as entire bottom area so it looked like new. I then dissambled with fireplace area and thoroughly cleaned burner. I did notice this white stuff on thermocouple; pilot and thermopile and I cleaned those to new with some cleaner and light sanding. I then wiped entire unit inside spotless so it to looks like new. I then re-assembled and through switch and it worked like new. So after 20 minutes I shut off and then turned on again and it started to run intermittantly again. I then shut off and turned on after 15 minutes and it ran for 5 hours no problem. I then shut off and turned on again and for remainder of evening hours it ran with intermittant on and off sometimes restarting itself. Again the pilot is always on. So I shut it off for good for evening.

So this AM turned on again and it has been running flawlessly for past few hours.

In the end I believe it is semi-fixed. Just can't figure out why it does not work flawlessly on demand. Again during daytime hours it has been running great. Don't know if this is an airflow issue; or requires a new thermocouple or thermopile. They seem easy to replace based on what I dissambled yesterday.

Looking for some help at understanding what might be cause. According to google most service techs are coming to house and installing expensive parts but still does not fix issue. I would like to exhaust everything prior to calling in service tech.

Any thoughts here would be greatly appreciated.

Submitted: 6 years ago.
Category: Plumbing
Expert:  Jerry replied 6 years ago.
Welcome to JA! New thermopile and new wall switch will fix this 99% of time. If you have digital multi meter I could have you run some tests.
Jerry and other Plumbing Specialists are ready to help you
Expert:  Jerry replied 6 years ago.
There are many things that can cause low millivoltage production.
1. Weak thermopile.
2. Weak or dirty pilot flame.
3. Floating or dancing pilot flame. Usually caused by venting problem.
4. Dirty or worn contacts on wall switch.
5. And lastly worn control valve. This is least likely.

If you can get a multi meter I can run through some tests for you. But usually changing the thermopile and wall switch will fix this. That is if your pilot flame is engulfing the top third of the thermopile and is sharp flame.

I believe your cleaning of the thermopile gained you some voltage but not the needed for complete fix.

Edited by Jerry on 12/23/2010 at 9:40 AM EST