I having been having some type of furnace/thermostat problem on my Janitrol GMPN-080-4 gas furnace. Thought the problem may be a thermostat problem, so replaced my old Honeywell Programable Thermostat with a new LUX Programmable Thermostat. Problem continued, so contct LUX. After much testing, LUX determined that the Thermostat was faulty. They replaced with a like LUX Thermostat which I installed. Problem continued, so I replaced the LUX Thermostat with a new Better Honeywell programmable thermostat. I have also replace the thermostat wiring from the thermostat to the furnace. However, the problem persists. I have been working with a service tech from Honeywell to help determine the problem. After much testing, we have come to the conclusion that the problem appears to be a furnace system problem, and not a thermostat problem.
The - The furnace fan automatically will turn on, without any heat nor cool. On several occasions, I have had the sytem turned off - no heat, and the furnace fan would still come on. With the nice cool evenings, I have shut the furnace system off at the thermostat, so no cooling system. This afternoon, the furnace fan came on. Appears the fan runs for about two minutes give or take. It is like the furnace has a mind of it's own. When the furnace fan came on, as instructed by the Honeywell Tech, I removed the face plate of the thermostat, but the furnace fan continued to run. The thermostat "fan setting" is set on "Auto", and not on "Circ", so it should only run when the heating or cooling system is on.
I am now suspecting that the control board could be the problem. Is there a way to check before spending alot of $$ for a replacement?
Any other ideas?? My next step is to have a heating/cooling specialist come look at the furnace, but I wanted to get input first.