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01-02-2022, 10:54 AM
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#1
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Junior Member
Join Date: Dec 2019
Posts: 7
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Dometic Furnace wont stay on
I have a Thor Outlaw 37RB with a Dometic 35000 BTU furnace. The problem that I am having is when the furnace turns on the following happens.
1. First Blower turns on for a minute or so.
2. Igniter lights and furnace begins to heat
3. Within less than a minute the furnace shuts down.
I know it is lighting because I can feel the heat coming out of the outside exhaust.
I recently had to replace the Burner head because Mud Dobbers had gotten in and filled it with Mud. I did get a screen for this but not until after the burner was replaced. This work was performed by a RV service company.
It did work temporarily a few times after the burner was replaced but just within a couple weeks it has developed this problem of shutting down.
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01-02-2022, 11:04 AM
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#2
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Senior Member
Join Date: Nov 2015
Posts: 26,810
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1. First Blower turns on for a minute or so.
*Purge Cycle
2. Igniter lights and furnace begins to heat
*Flame Ignites/proves it lit or it would shutdown within 6-7 seconds
3. Within less than a minute the furnace shuts down.
*Heating then tripping
What error code on circuit board (flashing LED)
Suspect it will be 2 flashes/3 second pause repeat
Limit Switch/Airflow fault
Limit Switch....opens when heat exchanger is overheated due to lack of proper airflow thru it
Could be obstructed air intake/exhaust
Could be obstructed return airflow back to furnace
Could be overfiring....high LP System Pressure
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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01-02-2022, 11:40 AM
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#3
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Senior Member
Winnebago Owners Club
Join Date: Aug 2012
Posts: 465
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It sounds like inadequate airflow to cool the heat exchanger. Since the furnace lights after the purge cycle, there is adequate airflow to 'make' the sail switch, and allow the gas valve to open and light the furnace. However, if there is not enuf cooling airflow (ttransfer heat to the coach) then the heat exchanger will reach it's upper temperature limit and shut the gas off.
I assume the blower continues to run but there the burner is tripped, which it will do to cool the heat exchanger then it will trip after a few minutes. If so, check to assure all the furnace vents are clear, and that none of the vent hoses are blocked. If they are all clear, then you need to check the blower operation.
Or, you say 'the furnace begins to heat'. Does this mean the blower is blowing WARM air and the exhaust is HOT? Or does it mean you hear some gas flowing? If the flue exhaust is not HOT, and the air into the coach is not WARM, then the thermocouple has probably failed, which will trip the furnace completely. This is not uncommon and is an esy fix.
__________________
Skip Y
2010 Journey, 2015 Equinox
Location: MI
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01-02-2022, 01:00 PM
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#4
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Senior Member
Join Date: Nov 2015
Posts: 26,810
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Just for clarification.......
No thermocouple used on RV Furnace
Spark Electrode has dual functions
*Provide High Voltage for ignition
*Return path for Flame Proving Signal (flame rectification)
*******No Flame Proving Signal within 6-7 seconds Circuit Board shuts down DC to gas valve. Will make 3 attempts at ignition the lock out
LED Flashing ---error codes on circuit board???
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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01-02-2022, 01:20 PM
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#5
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Junior Member
Join Date: Dec 2019
Posts: 7
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Quote:
Originally Posted by Skip Y
It sounds like inadequate airflow to cool the heat exchanger. Since the furnace lights after the purge cycle, there is adequate airflow to 'make' the sail switch, and allow the gas valve to open and light the furnace. However, if there is not enuf cooling airflow (ttransfer heat to the coach) then the heat exchanger will reach it's upper temperature limit and shut the gas off.
I assume the blower continues to run but there the burner is tripped, which it will do to cool the heat exchanger then it will trip after a few minutes. If so, check to assure all the furnace vents are clear, and that none of the vent hoses are blocked. If they are all clear, then you need to check the blower operation.
Or, you say 'the furnace begins to heat'. Does this mean the blower is blowing WARM air and the exhaust is HOT? Or does it mean you hear some gas flowing? If the flue exhaust is not HOT, and the air into the coach is not WARM, then the thermocouple has probably failed, which will trip the furnace completely. This is not uncommon and is an esy fix.
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Thanks for the quick responses.
Yes the Blower is blowing warn air and heat is coming from the exterior vent.
I will get in and check the duct work that sounds likely a the guys working on it were having a lot of difficulty getting the ducts reconnected.
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01-02-2022, 01:21 PM
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#6
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Junior Member
Join Date: Dec 2019
Posts: 7
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Quote:
Originally Posted by Old-Biscuit
1. First Blower turns on for a minute or so.
*Purge Cycle
2. Igniter lights and furnace begins to heat
*Flame Ignites/proves it lit or it would shutdown within 6-7 seconds
3. Within less than a minute the furnace shuts down.
*Heating then tripping
What error code on circuit board (flashing LED)
Suspect it will be 2 flashes/3 second pause repeat
Limit Switch/Airflow fault
Limit Switch....opens when heat exchanger is overheated due to lack of proper airflow thru it
Could be obstructed air intake/exhaust
Could be obstructed return airflow back to furnace
Could be overfiring....high LP System Pressure
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I will look for the circuit board I did not see that during my initial inspection.
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01-02-2022, 01:30 PM
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#7
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Senior Member
Join Date: Nov 2015
Posts: 26,810
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Remove exterior panel....full access to components
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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01-09-2022, 09:19 PM
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#8
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Senior Member
Join Date: May 2019
Posts: 228
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Had a similar issue with my furnace a couple years ago.
In my case, the reset switch/breaker on he furnace would trip within a couple minutes of furnace igniting and running. Switch felt “weak” when I would reset it. After several occurrences, I pulled the furnace out of the basement and replaced the switch. New switch was much more “stiff” to trip and rest by hand right out of the box. Also replaced the high limit switch while the furnace was on the bench just in case/just because; very inexpensive.
Minimal cost in parts….around $20 plus shipping at the time from what I recall. Hardest part of the job was becoming a contortionist to get to the furnace to remove it.
Good luck and let us know the outcome.
Safe Travels
__________________
Nonnie & Poppy
Crandall, Texas
2016 Keystone Alpine - 2019 Ford F350 DRW
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