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Furnace will not turn on unless I toggle the switch

2190 Views 8 Replies 3 Participants Last post by  danpik
Howdy all, my problem can not be all the difficult.

About 1 month ago the furnace would intermittently not turn on when the thermostat called for it. Sometimes it would. I toggled the Heat/off/Cool switch from heat to off and back to heat and the furnace would immediately kick on. I assumed the thermostat was faulty so I changed it and now we have to toggle the switch every time. The thermostat appears to be working correctly as it calls for heat when it should, it just wont trigger the furnace to come on. Toggle the switch and the furnace kicks on and off when it should.

Any and all help would be appreciated. We do have the furnace checked out annually and this years check-up showed no signs of any issues. Just trying to avoid a service call if the issue is simple.

Thank you.
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Toggling the switch is resetting the power to the circuit board which is locking out because of a fault. Post the brand name and model and serial # here. There should be a viewing window in the furnace door, look in and you will see a flashing LED which gives an error code. Code should be on the back of one of the doors.
Thanks for the reply. I have 2 doors on the front. The upper door exposes the controls and combustion chamber and the lower houses the fan and filter. No blinking LED is visible and there are no codes on either of the doors.

Furnace is a Ruud

Model number

Serial number
GN3D108 M46863415
inside the lower compartment is where the controll board usually is. That is where the blinking LED should be located. When you remove that door there is a switch that will release. you will have to manually push and hold it to get the furnace to start with the door off. On the board you can observe the flashing of the LED. Inside that door or the upper one should be the code legend
Thinking maybe I missed it, I just looked again. There is no control board, flashing LED in the lower compartment or error code on the door. The lower door does have the wiring schematic on it, but no error codes. I do know the furnace was installed in the early to mid eighties, if my memory serves me well.
the OLDER Ruud/Rheems have a circuit board but no viewing window for some strange reason. If it has LEDS on it then the code is buried in small print on the edges of the wiring diagram. Opening the door erases the code so you may have to put duct tape on the door switch to hold it closed so the next time you open the door the switch stays on and the code does not get erased. at over 20 yrs old that furnace may be near the end of it's road and spending a whole bunch of repair $$ is not worthwhile IMO. may want to get a Pro to check it.
Yeah, I will probably end up having it looked at. Thanks for the help.
can you post a picture of the unit with the doors off?
can you post a picture of the unit with the doors off?
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