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Old 03-13-2019, 07:18 PM   #1
Bear6201
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Dometic furnace "Short Cycling"

We own a 2018 3731 Montana front living room fifth wheel. The dometic furnace started giving us fits just before the first of the year. We called a local RV Montana dealer and they sent on a mobile tech and he diagnosed the problem as being the sail switch. Which is the switch that detects the blower operating prior to igniting the flame. That switch was replaced after two visits costing us $240 in labor.

The problem continues and they believed it was the circuit board that was bad. Dometic was very cooperative and sent a new circuit board and it was installed. It did not fix the problem.

The furnace short cycles in that it will ignite the burner which will burn for approximately 10 seconds and then shut off fan will continue to blow and then you can hear the furnace attempt to ignite again it will for about 10 to 20 seconds and shut off again repeatedly

Any insight to after the sail switch and the circuit board have been replaced what the heck could be next on the repair or replace list to get us back in operation!!��
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Old 03-13-2019, 10:47 PM   #2
rohrmann
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With everything that's been replaced, it's hard to believe someone hasn't verified that there is sufficient gas flow to the furnace. Your water heater and your stove can still work on much less gas than the furnace, so that isn't a good diagnostic check. Your regulator may be bad, or you might have a restriction in the gas line somewhere, or you may have a bad pigtail from one of the gas cylinders. I would be making sure there is a good propane source all the way to the furnace.
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Old 03-14-2019, 10:42 AM   #3
jeffba
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Originally Posted by rohrmann View Post
With everything that's been replaced, it's hard to believe someone hasn't verified that there is sufficient gas flow to the furnace. Your water heater and your stove can still work on much less gas than the furnace, so that isn't a good diagnostic check. Your regulator may be bad, or you might have a restriction in the gas line somewhere, or you may have a bad pigtail from one of the gas cylinders. I would be making sure there is a good propane source all the way to the furnace.
maybe try forcing a switch over to the other tank.....
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