I have a Lennox furnace Heater furnace in my house. The problem is when I open the gas, the furnace light will not lit until I switched the power On and the fan continuously run (24 hours) even when the house temp reaches the desired temp setting. If I turned off the Power switch, the furnace light will go off (No light). I put in a new thermostat but the fan continuously run 24 hrs. Is there something wrong with my fan relay?

You have both a fan switch on the plenum for low speed on heat and the fan relay which runs the fan on high for air conditioning. Something could be wrong with one of them sticking closed (the contacts stuck together). You will need a meter to check it out. You may be able to tap it and get the contacts to unstick and as some relays have two sets of contacts you can move the wires over to the second set contacts and you are good to go. The fan switch you will need to check. It has a cover and a dial under the cover.

Hi Tom,
I do not have an air-conditioning unit, only a heating unit. I will tap the relays as per your suggestion. The furnace blower fan runs contionuously 24/7. The digital thermostat for the fan is set in Auto mode. I will take a photo of the furnace and post it and hope, you response back.

Appreciate your help and have a good Holiday as well.
Cheers!!
Nedg

Send me an email if you want.