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Heating, Air Conditioning, Fridge, HVAC/janitrol furnace wont star....t its in the 30's here


I have a janitrol gpd100-4 gas furnace that's acting up...
When it goes to turn on everything is normal the blower starts and the glow plug heats..
then when the gas is supposed to come on several things might happen.
1. the glow plug will stay on for minute the shuts off or
2. the gas will ignite normally but only for a quick puff or as long as a few seconds then shuts off or
3. the gas will ignite and stay on for a few minutes then shuts off or
4. the gas will turn on and it will cycle on and off like it should but it will still shut down after an hour or two (this only happened once) I thought I fixed it at this time..
The control board error lite either will stay on solid all the time while its plugged into the wall or it will blink once very slowly.
I replaced the ignitor coil last spring, and I just cleaned the sensors both the single wire solid metal tube by on the left hand side of unit ( I think this the flame sensor ) and the 2 wire dime sized flat unit in the middle of the unit. I think this is the temperature limiter sensor switch ( I used fine steel wool to clean them.....)

Hi Bruce, You are right on, the flame sensor is the one with the single wire. The dime size switches are the "roll out switches". This is to detect flame rolling out of the combustion chamber. It sounds to me like your gas valve is failing. They will act this way sometimes before they fail.

Error light blinking once means ignition failure.

Also check the burners for restrictions. Sometimes bugs or spiders get inside. If you know anyone with a manometer you can check the gas pressure. There is an adjustment on the gas valve. The pressure  should be 3.5" for natural gas and 10.5" for propane.

Let me know if you have more questions.

Heating, Air Conditioning, Fridge, HVAC

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Jim S.


I can answer questions on gas or electric furnaces, ac units and heat pumps. I don't work on boilers,chillers,or home appliances.


I have been in the HVAC trade for over 35 years. For the past 15 years I have owned my own business. I am semi-retired so I can answer questions in a timely manner.

I attended trade school for 5 years on weekends and evenings. This was very hard to do, but well worth it!

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