Janitrol heaters can be dangerous things and you should only mess with them if you know what you are doing. Since you have asked the question here, I might assume you don't know what you are doing and as such I would advise you to take it to a qualified technician. There was a case of a Janitrol heater exploding in flight, blowing the nose off a piper Aztec. Luckily for the pilot, the good old Aztec has a tubular metal frame at the front, which supports all the necessary structure including the nose landing gear. He was able to fly the aircraft and land safely, although it was a bit cold and draughty.
The Heater has a built in logic sequence. If any parameter fails it will not start. First it needs combustion pressure which is supplied by the fan. Then it will check the overheat switch and if it is cold enough it will start the ignitor. If all the ducks are in a row it will finally allow the fuel to be injected, but if the fuel pressure is not sufficient the fuel solenoid will not open. If the fuel is injected with no spark, any subsequent spark will blow it up. That is why you don't mess with it. Testing different items out of sequence can cause the item to stop or start at the wrong time. If at any time the start sequence is interrupted, the whole start sequence will start again from the beginning after at least one minute of purging air has been pumped through the unit by the blower fan. If the fan is tired or the airflow has been restricted or too much fuel is injected, the unit will overheat and will automatically switch off the fuel. The fan should continue to run, but generally a manual reset is required to alert the operator that an overheat condition existed and may still exist.
Hope this helps.
on Mar 02, 2021