Furnace Won't Fire

paintr56

I have a work shop in my barn. I have installed a used lenox model # G1604/5-125-1 in the shop it ran great for about 6 weeks now it won't fire. It has an electric start and the pilot light comes on when the thermostat is turned on but the gas valve never opens for the main burner. I have used a volt meter to try to determine what is happening. By using the shut off switch on the door to turn it on and off I got the following information. The vent fan comes on then on the controll box the leads TH ( induced draft), PV , and the senser wires all have power. The ignition, TR, MV, and Mvpv leads do not have power. Any ideas on what the problem could be? I would be glad to try and get more info if it would help just ask the question and I will try to answere. Thank you for any help you can give.

Jim Bunton Just a painter

HVAC Doc

I would start off by cleaning the pilot/flame sensor assembly. It may have enough of a signal to prove the flame is lit, but not open the gas valve. The next thing would be the ignition contol is bad not allowing the pilot lit signal through to open the gas valve.

paintr56

HVAC Doc,
Thank you for the response I cleaned the senser and no change. Is there a way to check the ignition control or just change it and see if that solves the problem?

HVAC Doc

Since you have no power going to your TR or MV leads even after being cleaned, that is a pretty good indication the module isn't switching over after the pilot is established.

paintr56

Thank you
I ordered a controller today I'll know in a few days if that was it

Jim Bunton

paintr56

I installed the controller this weekend it solved the original problem. Now I have a new one. The furnace is in a work shop that I only want to heat when it is in use. The furnace fires then the thermostat that controls the blower fan heats up and the blower comes on this draws cold (20 degree) air into the furnace the thermostat drops and the blower shuts down. With the old controller the flame would stay lit and the cycle would repeat until the furnace room got warm and then things would be great. With the new controller the burner shuts down when the blower shuts down. The contoller is not identical it was cross refferenced as the correct replacement. I know under normal use this would not be an issue. currently I am manually resetting the thermostat to recycle the furnace until it catches up. Any tricks to do this outomatically?

Jim Bunton

Bestheating

Try wiring in a thermostat which has a manual ON for the fan position. It will take 3 or more strand wire. Turn the fan to constant on, while it is starting up. It will make the blower cycle less. Remember that a furnace is only designed to condition the air according to it's rated tempreature rise. Most often, about 55 to 70 degrees from one side of the furnace to the other.
Larry

paintr56

Thank you for the responses. I think I have it up and running. I changed the thermostat and it seems to be working. The reson I am not sure is we have been having very warm temps.

Jim Bunton