central-heatingfurnaceheatheating
I’m having issues with my furnace sometimes not kicking on.
I hear the furnace start, But then it will not fire.
However, If I go down to the basement and flip the power switch off and on the furnace starts and runs great.
It happens at least a few times a week.
Is the problem in the thermostat or the furnace?
Where should I start troubleshooting?
It is an older Natural gas, forced air furnace that works great when it is functioning properly.
Installed in 1995, I think its a Honeywell.
I had the exact same symptoms with my natural gas furnace, and it turned out to be the flame sensor.
It's an L-shaped metal bar (but can also be straight, depending on model) that detects if there are flames actually coming out, and turns off the gas if not. It had a white high-temp wire connecting it to the control board. Taking it out, cleaning it with some steel wool fixed the problem for me.
If yours is like the above, you'll only see the back part of it and the bracket, as the L-shaped end is inside the heating unit.
Can you look at the furnace during the time it is blowing cold air and see if the flame is on?
The thermostat has the ability to control the fan, but typically the thermostat sends a "turn heat on" signal to the furnace and the furnace controls are setup to turn the flame on for a X amount of time (to warm up the air) and then turn on the fan once the timer expired (so the air coming out of the vents is not cold). When the heat is turned on is the flame and fan going on at the same time?
Not sure about your furnace, but some have a couple of LEDs that are lit up and can be used to read a status or error codes. If you have the manual you could try to decipher the code while the cold air is running and see if it gives you a clue.
I would start by trying to figure out if the problem is with the thermostat or the furnace by installing a new thermostat and seeing if the problem goes away. If the problem is still there you can just return it. I had a furnace issue where it was going off randomly and would work in heat mode but not cool mode. It turned out that the thermostat was bad and sending intermittent signals.
Best Answer
Your furnace controller board is very likely indicating a trouble situation and shutting itself down. This is the equivalent of a car turning on its check engine light and not wanting to move. Shutting the main power off clears the error code and allows it to work temporarily but doesn’t fix what’s actually at fault.
First, change out your furnace filter. Many error codes are simply because the homeowner never changed the filter. Check the manual to see if there’s a filter timer reset button.
If the shutdowns still happen then the next time the furnace shuts down, keep the power on to the furnace so that you can read the error code. Your furnace should have a visible status led that is blinking (otherwise carefully take the cover off your furnace, avoiding any live wires, and look at the controller board). Count how many times the status led is blinking each cycle (sometimes how quickly it is flashing is also important). Reference your service manual to diagnose the error code. You may have a faulty sensor, sticky motor, bad controller board, too many closed dampers, a blocked air return, incomplete combustion, cracked heat exchanger, blocked condensate line, etc etc. some of these things are life-critical situations. The blickenlights will tell you.
Ps. Since this is a gas furnace, make sure your carbon monoxide detectors are working and don’t continue to operate it in this unstable and potentially dangerous state. It could be leaking carbon monoxide into your home which leads to permanent nighty-nights.