Hello beeman.
Does your furnace have a terminal board where the tstat wires hook up? r,w,g,y,c
Billy
When you say it wont shut off are you referring to the fan, or the burner?
For process of elimination..I would remove the thermostat from the wall. Twist the 2 wires together, this will bypass the stat operation and turn the furnace on. Then after it is running I would take the 2 wires apart and then see if the burner shuts off...and then the blower when it cools.
If the burner turns off, then the problem is within the stat. Make sure the wires in the stat mount back on R & W, If the burner stays on after you separate the 2 wires at the thermostat, then you have a stuck relay in the furnace.
I believe I have a heat controller manual. Let me look real quick and I can give you the link to where I keep info for online retrieval. This will just require following the wire on a diagram.
http://www.mediafire.com/?nn1clezg0tt
I think this is the one you need. Also reverse elimination...if the wires are apart at the stat and burner still running, take wire off gas valve. Then follow wire back from valve to the relay.
Did you get the manual from that link I sent? I am going to look at it now and give you my suggestions. I will just be a couple minutes.
All right, In the Heat Controller manual I gave you the link to, there is a troubleshooting flow chart. I followed it for your situation and it said to replace the gas valve.
HVAC Mechanic
State Licensed Mechanical Contractor, Heating, Cooling, Oil Burners, Heat Pumps, Boilers, Geothermal