Thermocouple Problem?

[bobjoek]

We have a Majestic direct vent fireplace using propane. When lighting the pilot, the instructions state to hold in the pilot switch for at least 30 seconds in order for the pilot to stay lit. With our fireplace, I can release the pilot switch immediately upon lighting the pilot and the pilot stays lit. Does this indicate a defective thermocouple?

Bob

 

[Bioburner]

If you snuff the flame and it still spews gas after 30 seconds then you have a big problem. Usually one can hear the release and the gas shuts down. Maybe its the thermopile releasing the magnet.
Welcome to the site. Not my usual dept(pellet)but I approved the post for viewing. Someone should chime in and help

 

[barmstrong2]

Will the pilot light without depressing the pilot knob? It is unusual that you could release the knob immediately and have the pilot remain lot. I'd be concerned the gas valve is malfunctioning.
As bioburner suggested, test the pilot safety. After the pilot is lot, turn the gas supply of with the shut off in line, it should be located in the control box and will be a 1/4 turn valve before the gas valve. This will shut the pilot off. Within 30 seconds, you should hear a "click" from the gas control.
If you do not hear that click, or, if you can light the pilot cold without depressing the knob, the gas valve is malfunctioning and there is no pilot safety.
That would be an extremely unusual thing to happen, as they always fail the other way. I don't believe I have ever found a magnet stuck open. Always fail to stay to remain open when they should.

 

[Tech Guru]

yes, the 30 second Drop-out test is key, as detailed by bioburner and barmstrong. I have on plenty of occasions had pilots hold with much less time than 30 seconds. That is more of a catch-all time frame for thermocouples which may heat up (and thus generate current) more slowly. If you get that pilot lit, let it run for a good minute or two then blow it out, if your pilot gas flow does not 'click' off within 30 seconds, then you could have a valve problem. (very rare) Of course, in a standby (off) mode, any pilot gas flow with the knob not depressed in the pilot position would also represent a valve problem...

 

[bobjoek]

Many thanks for the responses. I did try your suggestion to run the pilot for several minutes, then blew out the pilot flame. It took 50 seconds for the pilot gas flow to stop. Then I heard a click, not in the Honeywell control, but in the vicinity of the thermocouple and thermopile. I tried this several times, each with a 50 second delay with the gas shutoff. Turning the control to the off position immediately stops the gas flow. Is 50 seconds way too long? If so, do I have a problem with the thermocouple/thermopile or the Honeywell control?

 

[barmstrong2]

50 seconds is OK. As long as it does shut off. In your OP, you said you can light the pilot and immediately release the knob and the pilot stays lit. Do you really mean immediately? That is the concern. The thermocouple is no mysterious or magical thing. It's simply a rod made with 2 different types of metal which will expand at different tastes with heat, thus creating a small electrical current which will hold open the magnet in the gas valve. If the pilot will remain lit ---immediately--- without any time to build the millivolts, from a cold start, that is cause to check the valve further. If it takes 15 seconds, instead of 30, that's OK.

 

[bobjoek]

50 seconds is OK. As long as it does shut off. In your OP, you said you can light the pilot and immediately release the knob and the pilot stays lit. Do you really mean immediately? That is the concern. The thermocouple is no mysterious or magical thing. It's simply a rod made with 2 different types of metal which will expand at different tastes with heat, thus creating a small electrical current which will hold open the magnet in the gas valve. If the pilot will remain lit ---immediately--- without any time to build the millivolts, from a cold start, that is cause to check the valve further. If it takes 15 seconds, instead of 30, that's OK.

I can light the pilot and it will stay lit if I keep the knob pushed in for only 1-2 seconds. That is my concern as previous experience is that 15 + seconds were necessary to keep the knob pushed in.

Bob

 

[barmstrong2]

From a cold start, knob set to PILOT, not pressed, is there any gas at the pilot?

 

[bobjoek]

From a cold start, knob set to PILOT, not pressed, is there any gas at the pilot?

No gas until I press in the knob while set to pilot.

Bob

 

[barmstrong2]

No gas until I press in the knob while set to pilot.

Bob

Then I wouldn't worry about it.