Hi,

I have a 80% efficient furnace and I am having the following trouble with the heat.

The draft motor starts running the moment I power on the furnace. Its had been running during the summer time also when the I just was using AC. Being new to these things I did not realize that it was a problem.

Issue:
When I power up my furnace and it reaches the set temperature, thermostat instructs the furnace to stop, and it stops. However, The draft motor keeps running.

When the thermostat instructs the furnace to start, the furnace LED indicator blinks three times (which is described as "pressure swtich failed to close"). However, at that time if I power off the furnace and wait for few seconds and then power it on again, it works until next time the thermostat tells it to stop. I have to manually do this every time I need to heat my house.

Any help is appreciated.

Probably a defective pressure switch. Test it.

Thanks for your response hvac1000.

Can you provide more details on how to test the pressure switch ?

Can the furnace start up in the first place with a faulty pressure switch?

Thanks again !

Usually there is a round metal object with a tube going to it. Remove the tube and blow through it to make sure it is clear. Next take a meter and check for voltage going through the switch. Just use the frame as ground and test both sides of the switch with one side of the switches wires removed. This will tell if the switch is stuck closed.

Another way and a bit safer is to remove the wires off the switch and mark them as to where they came from. Then use a ohm meter and measure across the contacts. If the contacts are closed you know you have a bad pressure switch. NOTE the power should be off anytime you are removing wires or testing with a ohm meter.