After recently purchasing a 1984 25' Soverign, we've had a problem with the heater not shutting off after it has run for an extended time. If the temperature rise needed (run time) is not much, all is well, but...if it runs for about 10 minutes or more, it will not stop. I don't mean that the fan simply continues to run, the flame also does not extinguish and heat output continues. Turning down the thermostat or even removing it completely from the circuit still makes no difference. Ive found that turning off the gas supply at the inlet side of the furnace is the best way to stop the run away condition. I've seen lots of post on all variety of non-starting heaters but this one seems unique since it starts and runs fine. Has anyone dealt with this problem before or care to speculate as to the possible cause? My gut feeling is that it will be a bad control module not telling the gas valve to close therefore everything continues to run because the flame does not extinguish. I suppose it could also be a faulty gas valve but if the later were the case, I would think gas might continue to flow even after the flame went out on a short duration burn. Then again...the burn would not end if the gas were still flowing. Sort of chicken or the egg dilema with that possibility I suppose so Im leaning more toward the module and not a mechanical malfunction of the valve.
Please lend any thoughts or experience.