My daughter's gas furnace often doesn't turn on when the thermostat is calling for heat. She can get it to do it by turning the heat off and then back on again. I also noted, when at her house, that when it was in this state (calling but not on), when I pulled off the lower panel to the furnace it released an interlock switch, when I reinstalled the panel it immediately started the furnace. It did this several times in a row. Did this interlock switch reset the controller?

Is there something obvious to look for or is it likely to be an intermittent furnace controller PCB?

Thanks

If the furnace malfunctions, the circuit board control logic will impose a timed "lockout". Interrupting power or thermostat demand will often cancel the lockout. Look for a status LED on the board - it may provide clues if present.

If the furnace malfunctions, the circuit board control logic will impose a timed "lockout". Interrupting power or thermostat demand will often cancel the lockout. Look for a status LED on the board - it may provide clues if present.

Thanks, that explains how it "seems" to recover.

Regarding the LED indicators. There are two green LEDs labeled DS1 and DS2. I did notice them but don't recall if I remember what condition they were in.

Could you give me an idea of how to interpert their meaning? Also does taking off the panel, which opens the interlock switch, change their state? I have attached a photo of these LEDs and have other photos that my be helpful including the schematic that was on the panel

Thanks for your help.

There should be a label inside the front panel with a description of the diagnostics. If power is interrupted, status code is usually cleared, so next time the unit malfunctions, check the status LEDs first.

There should be a label inside the front panel with a description of the diagnostics. If power is interrupted, status code is usually cleared, so next time the unit malfunctions, check the status LEDs first.

I had taken a photo of the inside of the panel. It is attached. I have zoomed and panned over it and can't find the LEDs even shown as part of the system. Seems odd. Also, no diagnostic summary. Last, the LEDs are not viewable w/o removing the lower panel. Doing so opens the interlock switch. The only to view the LEDs when a failure occurred (it would seem) is to leave the panel(s) off and tape the override switch closed. I'm not sure that would be a good idea.

Thanks again for your time and any additional thoughts are appreciated.

Be well.

Cheers,
Ray
P.S. Sorry the photo could not be rotated, as an attachement.