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Heating, Air Conditioning, Fridge, HVAC/furnace starts but gas wont stay lit


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.....)

Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.

Flame sensor could be bad, not just dirty.
Gas valve not opening properly.
Burners dirty.
Gas pressure too low.

The problem is going to be gas or control related.  Hard to say without hands on.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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