Furnace

[Conrad]

New project for me.    The furnace.  The unit powers up when the thermostat is set to 'call' for heat.  The spark works, the flame comes on for about 4-5 seconds then I hear a click and then it shuts down.  I have observed the flame and verified that the entire flame tube is working and that the flame is a nice blue color.  I suspect either a circuit board problem or the temp sensor mounted on the outside of the heat chamber.  The ability to heat has been an escalating problem over the years.  It used to take me a few starts to get the furnace going, then a few more... I thought that it was a leveling issue.    

Has anyone had similar problems?  I can bench test the unit with bottled LP.

[egibbons]

Take a good look at that over-temp sensor. It shuts down the furnace when over-heated (Like in case the blower stops and excessive heat builds up inside the heater. With age and exposure to heat, it may have gradually failed (worn out)until it is triggered with just a little rise in temperature. Can you use an ohm meter? If so, measure the sensor cold and after the furnace shuts down. You can temporarily bypass it for a bench test(disable the wiring or remove the sensor from its mount so it won't heat up). Confirm that the heater runs when it doesn't trigger. Do not use the heater without this important safety device! Try a good hardware store, a local air-conditioning/heating firm or the manufacturer for a replacement. Good Luck!

[Conrad]

I pulled the unit to work on it.  made up a LP hose extension.  Fired it up and it worked the first time!  I think that condensation may have gotten into the contacts.  Maybe my moving it broke through somesurface scale.  I can't figure any thing else.  Now I have a dry MOHO.

thanks