RV Repair: sub nt34s furnace wont light, gas valve, test light

Question
I bought a motorhome a couple of months ago and use the furnace a couple of times. It would heat alright but when the thermostat got to temperature the fan would shut off but the burner would stay on until i turned the thermostat off. It wouldn't do this it all the time. Now when I turn it on the blower comes on and there is some clicking noise but won't light. I had the board checked and it's ok. I also replaced the sail switch and limit switch and clean the electrode and gap was right. But it still won't light any clue what it would be.

Thanks, Rick

Answer
Sounds as if you might have a faulty gas valve. The reason it stayed lit is that it stuck open. Then when power was removed, it closed and will not open now. If you have a 12vdc test light, check for 12vdc at the gass valve when the igniter is trying to light the flame.

Jim