Heatilator GCDC80 won't light

[EWil]

I have a Heatilator model GCDC80 - the basic model without the flan blower or remote - a real basic model.

The flame ignites (or is supposed to ignite) but closing a basic wall switch - which closes a couple of leads in the valve.

The problem is that when I close the switch, the flame does not come on - or not right away. If I leave it on long enough, it may come on - or may go off. I have tested and don't have a bad switch (I have also tried using a piece of wire to short the leads.

How can I further troubleshoot this. Is there some power to the valve that causes it to open when the contact closes? Any troubleshooting assistance would be greatly appreciated. I know it is an old model, but I don't want to have to replace it yet.

Thanks in advance for the assistance.

 

[DAKSY]

Do you have a multimeter?
Set it to volts DC & take a reading on the TP & TP-TH (or TH-TP)
screws on the terminal block on the gas valve. With the pilot on &
the burner off, you should be getting a steady 550 mV.
Once the switch is thrown, the reading will drop to the 220 mV range & hold steady.
Report back with your findings. First guess would be your thermopile is on the way out.

 

[EWil]

Do you have a multimeter?
Set it to volts DC & take a reading on the TP & TP-TH (or TH-TP)
screws on the terminal block on the gas valve. With the pilot on &
the burner off, you should be getting a steady 550 mV.
Once the switch is thrown, the reading will drop to the 220 mV range & hold steady.
Report back with your findings. First guess would be your thermopile is on the way out.

Thanks for the super quick and helpful reply. Seems like my multimeter has walked. I will pick one up and report on the results.

 

[EWil]

Got a multimeter and tested.

Across the TP & TP-TH with the pilot on and burner off I get only 310 mV. After throwing the switch I only get 50 mV. Quite lower than expected.

Any ideas?

Thank you very much.

 

[DAKSY]

Replace the thermopile. A universal millivolt generator can be
obtained at most hardware stores for about $50

 

[EWil]

Thank you so much for your help. I read up on what the Thermopile is supposed to do and that makes perfect sense.

Turns out that I think I can get a part of Amazon for $13.99. The part number is 2103-512, according to the Heatilator parts list (http://downloads.hearthnhome.com/serviceParts/GCDC80.pdf). Amazon has a replacement here http://www.amazon.com/Heatilator-Heat-n-Glo-Thermopile/dp/B00MU5O59A. I really appreciate the help - it was so frustrating.

 

[EWil]

I have one further question - what is the best way to replace the Thermopile.

I see that the Thermopile wire is bundled with the bundle feeding the pilot light - from the access area on the bottom through to the interior of the fireplace. That area is plugged up but by rubber caulking.

Should I just remove that piece of rubber - it doesn't look like I will be able to replace it after tearing it away. Do I need to reseal it?

I was hoping to find some hints on the best method to do this, but I have not found anything. If anyone can provide or point me to some quick instructions - that would be very much appreciated.

 

[DAKSY]

You need a Philips screwdriver to loosen the two screws on the terminal block tp remove the thermopile wires.
They are marked as TP & TH-TP (TP = ThermoPile). Youwill need a 7/16" (or 11mm) open end wrench to loosen the
nut holding the TP into the pilot assembly. Sometimes it's easier to lift the pilot assembly off the burner slightly
- giving you enough room to get the TP out - by removing the screws that retain it.
These are usually 1/4" drive zipscrews.
Don't remove them until you have loosened the retainer nut on the TP.
Once you remove the TP from the pilot assembly, you should be able to slowly pull the two TP wires thru the
grommet & into the firebox.
If the grommet gets destroyed, don't worry too much.
They tend to dry rot after years in the firebox.
Push the new TP wires down thru the grommet & slide the TP into the pilot assembly.
Hand tighten the retainer nut. Re-install the pilot assembly & secure with the zipscrews.
Tighten the retainer nut & the Philips screws on the terminal block.
There is no polarity involved, so it doesn't matter which wire goes to the terminals.
You can use RTV Hi-Temp silicone in lieu of the grommet to seal the wiring holes.
Put the logs in & light the pilot.
PUT THE GLASS FRONT ON.
Take your milliVolt readings on the TP screw heads & adjust the PILOT using the adjustment screw on the front
of the valve - there is probably a chromed slotted screw covering brass slotted pilot adjustment screw...Remove it to make adjustments.
Again, you want a reading of about 550mV.
Turn the burner on & take a the mV reading. Should be about 220mV or so...
Let us know how you make out.

 

[EWil]

Thank you so much for those instructions. It appears to be perfect and exactly what I was looking for. I hope to get to this over the weekend and will definitely report on how it went.

I really appreciate the assistance.

 

[EWil]

Thank you again for your instructions. Access was a bit challenging, but with your instructions I managed to get the job done.

The new ThermoPile gives me just about 500mV unlit and 200mV when the burner is on. Not as good as your benchmark reading, but certainly much better than I had. The burner now goes on immediately.

In the past I have kept the pilot lot on throughout the year. Perhaps I should shut it off after the season - it will save a bit of energy and perhaps make the ThermoPile last a bit longer. The part is not expensive, but it is not the easiest to replace.

I really appreciate all of the assistance. It helped tremendously!

 

[DAKSY]

Glad to help.