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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22541
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Have a Mr.Heater Big Maxx serial number LN-2600450004883 and

Customer Question

have a Mr.Heater Big Maxx serial number LN-2600450004883 and when I turn it on the blower just runs no ignite attempt can't smell gas at all.
The green LED flashes 4 times which in my manual says "roll out switch(es) need to be reset or heat exchanger limit sensor bad" I believe I found the rollout switch it's about the size of a nickel, located just off to the left of the board and has two wires running to it and a little white button in the middle which isn't doing anything when I press it. How would I diagnose if the limit sensor on the heat exchanger is bad? I have a multimeter and tools here.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

hello, you can bypass the limit (mounted on front wall) just for testing.

Also at the board you can jump out circuits for testing..many of these boards have a high limit switch out....and then high limit switch in on the board.

Obviously if 24v leaves on must return on IN...

Commonly this is a fan issue or restricted air flow.....