Gas furnace only works sometimes?

Question

We have a gas furnace that only works sometimes.

The pilot light is lit. When the thermostat triggers the heater to come on, I do not hear the click that usually happens at this time, the flame does not ignite, and the fan never comes on.

It sometimes helps if I turn the thermostat off for about five minutes then turn it back on and turn up the temperature until it should click on. But when it's happening a lot, this only fixes it the first few times. After a few times, even this won't work. Then we just wait an hour or so and keep trying the above until it comes on.

I did already check to see if the thermostat was bad, by taking it off of the wall and touching the red and white wires together. Nothing happened, so I think the problem is other than the thermostat.

Answer 1

I recently had my furnace repaired, which was working intermittently. Although mine is a high efficiency furnace with an igniter instead of a pilot, the principle is the same. The problem turned out to be a sticking solenoid in the gas valve. The repairman told me that this was the first gas valve he had to replace in 19 years in the business, so it is not a common failure.

Nonetheless, you should check to see whether there is a voltage at the solenoid terminals on the gas valve. If there is a voltage (24V usually), and you have access to an AC ampmeter, check to see if there is any current. The solenoid may be burned open, or it may be sticking.

The fan is controlled by a thermostat in the furnace, not the thermostat on the wall. You should not expect it to come on until the furnace has heated up.

Answer 2

u may not be getting voltage to the furnace .take the thermo off the wall [shut off furnace] now jumper the white to the red .the furnace should come on .if so then u have abad thermostat [remember that the thermo wont shut the furnace off until u remove the white wire!

Answer 3

Sounds to me like you may have mentioned the area of the problem when you were talking about the cover, that initiates a restart when you remove it and put it back on. Is it fitting good and snug, held tightly in place? Because it sounds like the lever or button or whatever it is that is tripped when you remove the cover, is not being held tight in the position it needs to be in to make things work as they should. I'd investigate that possibility to it's end before buying any parts.

Answer 4

Perhaps a bad connection somewhere within the system?

Answer 5

go with Tech dudes answer he is right on.