Carrier Gas furnace shuts off at night

[fsds123]

This started happening last week to a Carrier electric start gas furnace that is about 14 years old

It will run fine all day long cycling on and off as needed, but then late at night/early in the morning it will shut off and the house will get cold. If I go into the attic in the morning and simply remove the cover and put it back on (releasing and pressing a switch in the process) it starts working again. I've cleaned all the connections/igniter/flame sensor with no luck.

I've called someone in to look at it (one morning after it shut off again) and they could not find anything wrong either.

Any ideas?

Also, does anyone know if the cover switch is anything more than just a safety switch...i.e. the cover has to be on to keep the switch pressed in order for the blower to work, but does it also reset something when released and then pressed?

Carrier model number is 58RAV095 13116

[fsds123]

It shut off again tonight, and I was able to get a better idea of what it is doing.

It will start the inducer motor, and the igniter will start to glow, but when the gas is supposed to come on it doesn't...and then everything shuts down. To get it to try the cycle again requires me to remove the cover and press the switch...it will keep doing this but the gas will not start.

In the mornings the gas does start...so I wonder if it is due to it being quite a bit colder in the attic at night?

Is there a temp sensor that can be too cold?

[Java_Bob]

bad sensor, or bad board. is there any flashing lights on the circuit board?

[fsds123]

Yes, there is a red flashing light on the board. 1 long flash follwed by 2 quick flashes.

When you say it might be a bad sensor, which one? There are what appear to be 3 of the round temp sensors...2 by where the gas lights on the right (one top one bottom) and another on the left side towards the top.

[Java_Bob]

LOOK AT THE DIAGRAM on you unit the code for those 3 lights should be on it, i am guessing flame sensor

[fsds123]

I'll check this afternoon when I get home, although I don't think it would be the flame sensor, since when it doesn't work the gas never flows and thus never lights. The igniter burns nice and bright and the inducer motor spins fine as well, just no gas.

[Java_Bob]

bad board then, not turning on pilot gas

[fsds123]

This is the code I am getting

21 GAS HEATING LOCKOUT - Control will NOT auto reset.
Check for: - Stuck gas valve relay on control or miswire to gas valve circuit.

[HayZee518]

I would have to check out the schematic wiring to let you know if that door switch does something other than just break the loop to your gas valve. those sensors you speak of are they about the size of a dime with a two hole bracket? if this is so they are a bi-metallic switch that serves as a limit switch temperature controlled. as they heat up they open -or- close depending on usage.

[hvacwiz]

Just check to see if you have 24v at the gas valve when it is suppose to lite, if you do and it dont fire, replace the gas vave. You DONT have any bad limits ,if you did it would never get to the point of the ignitor glowing. And by opening the door switch you are just cutting off the main power to the furnace and then reseting it when the switch is pressed in again, your furnace will then go through the sequence of operation again. More than likely you need a new gas valve.

[fsds123]

I replaced the board and have heat again.
Thanks for the help