I have a Intertherm M1M It runs great one time then gives a weak flame (after the flame goes out) after reaching temp. I changed the igniter/temp sensor (one unit). I replaced the main board also. Still the same problem.

Could it be the thermostat?



The thermostat should turn the system on and off. If you are having problems with intermittent flame you may have moisture in your line. I usually install drip legs after the shutoff valve prior to the furnace, water heater or range this traps the water. A drip leg is a T with a short section of pipe going straight down that is capped. This leg catches rust, and moisture. 1 drop of water in a gas valve can cause problems so I would check to see if you have a drip leg and if so shut the gas off and clean it. If you don't install one. I have had homes that had horrible moisture problems in gas lines and others that had almost no problems. Since you have thrown all those parts at it I would be looking at moisture as the possible cause.


Unless you're experienced in gas heater repairs I suggest to contact a professional service technician. Usually your gas service provider has trained techs on staff.

Here is the schematic with trouble shooting assistance for the model posted. Hopefully this PDF opens for you. If not, Google search your model with troubleshooting after it in the search bar...

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