Fireplace won't light, thermopile? Good voltage.

[maxash]

Hello All - new to the forum. I have a 11 year old Napoleon natural gas fireplace (GDS20N). It has worked great all these years, no issues. Recently, the thermostat (simple mercury switch style) stopped turning the fireplace on as it should. Thinking perhaps that was the issue, I disconnected the 2 wires from the thermostat and jumped them together. No luck. I tried the On/Off switch on the unit itself, and it worked the first time I tried it, but the second time I tried it an hour or so later, that wasn't working either.

Pilot light is on and has a nice blue flame. I checked the readings on the TP/TH & TP and I saw ~650mV, which from research seems fine. Just in case, I checked and cleaned the thermopile and thermocoupler as directed. Took a new reading after turning the pilot light back on and I'm at 720mV now. Seems a bit high on both readings, not sure if that's an issue?

I'm not really sure where to go from here. With a good strong pilot light, the unit in "On" position (I made sure the knob was not on "Pilot" still), and the readings seemingly high enough on the Thermopile... what could be the culprit?

Thank you in advance for any advice!

 

[maxash]

I just had a chat with the original installer. He said the valve might have gone bad, and that's a pain to replace according to him. Thoughts?

 

[DAKSY]

What happens to the vDC when you turn the burner on? Have you checked that?

 

[maxash]

What happens to the vDC when you turn the burner on? Have you checked that?

I kept my meter connected just now. With pilot on and burner at Off I get 675 mV, when I turn the unit to On, it drops to 112 mV

 

[DAKSY]

Replace the Thermopile. True Value carries a Universal MilliVolt Generator.
$50+. With the switch on, you should be at 220 +/- 20 mV.

 

[maxash]

Replace the Thermopile. True Value carries a Universal MilliVolt Generator.
$50+. With the switch on, you should be at 220 +/- 20 mV.

Thank you for the replies so far, I appreciate it.

I ordered a new Thermopile, should be here in a couple of days. Regarding the millivolt generator, are you suggesting that as an alternative for testing purposes?

I disconnected all the wiring from the valve and tested the TP to TH resistance. The reading was ~ 3.5 ohm. From my research, a SIT valve like mine is supposed to be 1.75-2.75 ohm, is that correct? If so, is this a sign the valve is bad?

 

[DAKSY]

Not sure which SIT valve you have, but, yes that reading sounds a bit high. It should read 0 - 2.6 ohms, with all leads removed.
Reading across the TP & TH terminals..Let's take it one step at a time. Replace the Thermopile & if you are STILL having issues,
you can move onto valve replacement. If you are planning to keep this unit for a number of years, you could always get a replacement
valve as a spare. Valves very seldom fail, but operation for 11 years is a long time, & failure is not out of the question...

 

[maxash]

Sounds good, will do. Hopefully the thermopile is here by tomorrow or Friday, and I'll swap that out first. Thanks again for the help. I'll report back as soon as I do that.

 

[maxash]

Success! Installed the new thermopile today, and everything seems to be working great again. I tested the voltages, and they're perfectly in range now as well. It took some work and learning, but I feel good having repaired it myself. Thank you for your help!