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Thread: M21 M22 empty switch problem

  1. #1
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    M21 M22 empty switch problem

    I have an M21 heater that has seen little use that I converted to internal tank use. I activated the empty switch and it always flashes empty no matter what. Does anyone know what goes wrong with them? I don't think it was ever used with an internal tank.

    I also have an M22 that I activated the feature on and it was working fine until last night when the tank ran completely empty. I put in a new tank and the light went out but after it started the burner the light came back on. Now it stays on and puts in on a 30 minute timer. Is there a common issue on these that make them stick or do they just fail? I am running ULSD if that makes any difference. I really don't want to take the front off the heater again to deactivate it like I did the other heater.

  2. #2
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    Have you checked the screen the tank sits on. If it has lint on it it will stop the fuel and cause an Empty Tank light. The switch can stick and that is a pain. ULSD is an OK fuel to run and is not the problem. If the switch sticks and you can't get it right you can disconnect it if you don't want to get another switch. I have never had to replace one of those switches, they are bullet proof. Tom

  3. #3
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    The screen is ok on it. I figured out the problem with the M22. The replacement tank I used is slightly caved in on the bottom so I think the fuel does not feed fast enough.

    As for the M21, I will have to test the float switch I guess. I don't think it was ever used with the in tank option so hopefully it is just stuck or something. I found that the switch can be removed without taking apart the heater so I am in luck I suppose.

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