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01-19-2018, 05:14 AM
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#1
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Senior Member
Join Date: Sep 2010
Posts: 297
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Suburban Furnace
Furnace is only 1 year old & has been heating fine. Thermostat is a Dometic 5 button control on the wall. Furnace has been running fine, last night at about 11PM it stops running (38 deg. outside). All led lights on thermostat are working & lit when going through each function, but furnace doesn't run. Gas tanks are all full & hot water heater works fine. I can cycle through all the modes & raise & lower temp setting, but nothing happens. I'm thinking the thermostat is bad. Any suggestion would be appreciated.
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2017 Grand Design Reflection 26RL
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01-19-2018, 05:29 AM
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#2
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Senior Member
Join Date: Sep 2016
Posts: 593
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Quote:
Originally Posted by countrypair
Furnace is only 1 year old & has been heating fine. Thermostat is a Dometic 5 button control on the wall. Furnace has been running fine, last night at about 11PM it stops running (38 deg. outside). All led lights on thermostat are working & lit when going through each function, but furnace doesn't run. Gas tanks are all full & hot water heater works fine. I can cycle through all the modes & raise & lower temp setting, but nothing happens. I'm thinking the thermostat is bad. Any suggestion would be appreciated.
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There might be a fuse that popped in the 12 volt panel. Check easy stuff first.
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2016 Leisure Travel Vans - Serenty
Toad - 2009 RAV4, 2WD with Remco Lube pump
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01-19-2018, 06:32 AM
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#3
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Senior Member
Mid Atlantic Campers
Join Date: Sep 2015
Posts: 509
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Mine quit after a 3400 mile trip. Long story short the thermostat wires running from the air conditioner to the furnace had broken. Replaced the old thermostat and ran new wires to furnace eliminating the old circuit.
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2008 CC 34RLSA / 2003 F-250 SD 6.0
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01-19-2018, 06:52 AM
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#4
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Senior Member
Join Date: Jul 2010
Posts: 5,309
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Mine quit working and turned out to be an inline fuse near the furnace. Mine is controlled by a Dometic thermostat that also controls the heat pump, not sure that matters though. I would check for a blown fuse.
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Tom
2016 Newmar Bay Star Sport 3004
2021 Jeep Gladiator Sport Willys
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01-19-2018, 08:15 AM
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#5
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Senior Member
Join Date: Sep 2010
Posts: 297
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Quote:
Originally Posted by wildtoad
Mine quit working and turned out to be an inline fuse near the furnace. Mine is controlled by a Dometic thermostat that also controls the heat pump, not sure that matters though. I would check for a blown fuse.
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All fuses ok! Pulled cover off thermostat & activated furnace. started up & ran fine. Plastic cover looks real cheap & perhaps wasn't contacting the little switches??? Running without cover for now. Thinking of replacing with new CT thermostat # 3316250.012 , maybe more reliable, only $38.
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2017 Grand Design Reflection 26RL
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01-19-2018, 09:12 AM
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#6
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Senior Member
Join Date: Sep 2016
Posts: 593
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Quote:
Originally Posted by countrypair
All fuses ok! Pulled cover off thermostat & activated furnace. started up & ran fine. Plastic cover looks real cheap & perhaps wasn't contacting the little switches??? Running without cover for now. Thinking of replacing with new CT thermostat # 3316250.012 , maybe more reliable, only $38.
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Glad you got it going. If the replacement T-State, or even current with cover off doesn't fix it, you might have the problem that I had. This is a very rare failure according to Suburban, but my unit would run one time with no problem, and just like yours, it would do absolutely nothing the next time T-stat called for heat. After extensive trouble shooting, it was determined that the sail switch stuck closed and would not spring back when the fan shut off. The control board just locks out the system when this happens (no fan and no ignition).
So how can that happen with spring tension on the sail switch? Well, believe it or not, the paddle on the switch was just touching the heat chamber when the fan blew the paddle back to the closed position (allowing ignition). When the furnace ran through its first cycle, the heat chamber expanded (as you would expect), and that contacted the edge of the paddle and held it in place so it would not drop back. A few hours later, the paddle would come loose enough from the heat chamber cooling and drop back under spring pressure. Also, the little vibration from just driving the rig would allow the paddle to drop back under spring tension.
We like to never figured this out (changed control board and went through entire diagnostic logic chart). Finally, I found out that simply banging on the furnace case with the heel of my hand immediately got it running. From there it was an easy fix.... just a mater of bending the paddle over about 1/32 of an inch. It has worked fine ever since.
... and by the way, this was a brand new unit. The RV dealer ran it before we bought the RV, but never ran it through a second cycle, so to him, it appeared fine.
__________________
2016 Leisure Travel Vans - Serenty
Toad - 2009 RAV4, 2WD with Remco Lube pump
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01-20-2018, 06:05 AM
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#7
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Senior Member
Join Date: Sep 2010
Posts: 297
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Quote:
Originally Posted by hoosierrun
Glad you got it going. If the replacement T-State, or even current with cover off doesn't fix it, you might have the problem that I had. This is a very rare failure according to Suburban, but my unit would run one time with no problem, and just like yours, it would do absolutely nothing the next time T-stat called for heat. After extensive trouble shooting, it was determined that the sail switch stuck closed and would not spring back when the fan shut off. The control board just locks out the system when this happens (no fan and no ignition).
So how can that happen with spring tension on the sail switch? Well, believe it or not, the paddle on the switch was just touching the heat chamber when the fan blew the paddle back to the closed position (allowing ignition). When the furnace ran through its first cycle, the heat chamber expanded (as you would expect), and that contacted the edge of the paddle and held it in place so it would not drop back. A few hours later, the paddle would come loose enough from the heat chamber cooling and drop back under spring pressure. Also, the little vibration from just driving the rig would allow the paddle to drop back under spring tension.
We like to never figured this out (changed control board and went through entire diagnostic logic chart). Finally, I found out that simply banging on the furnace case with the heel of my hand immediately got it running. From there it was an easy fix.... just a mater of bending the paddle over about 1/32 of an inch. It has worked fine ever since.
... and by the way, this was a brand new unit. The RV dealer ran it before we bought the RV, but never ran it through a second cycle, so to him, it appeared fine.
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Thanks for the info. I will check mine for the problem. As an aside I looked at the new replacement thermostat CT the contacts are enclosed in sponge & the RV place told me they wear out very quickly if used constantly. You can't buy the original replacement! Further, the RV place said Dometic knows this & is working on another model. Typical of failing parts, always another new model for more money.
__________________
2017 Grand Design Reflection 26RL
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01-20-2018, 05:07 PM
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#8
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Senior Member
Forest River Owners Club Ford Super Duty Owner
Join Date: Jul 2012
Location: So Calif
Posts: 3,521
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Quote:
Originally Posted by hoosierrun
Glad you got it going. If the replacement T-State, or even current with cover off doesn't fix it, you might have the problem that I had. This is a very rare failure according to Suburban, but my unit would run one time with no problem, and just like yours, it would do absolutely nothing the next time T-stat called for heat. After extensive trouble shooting, it was determined that the sail switch stuck closed and would not spring back when the fan shut off. The control board just locks out the system when this happens (no fan and no ignition).
So how can that happen with spring tension on the sail switch? Well, believe it or not, the paddle on the switch was just touching the heat chamber when the fan blew the paddle back to the closed position (allowing ignition). When the furnace ran through its first cycle, the heat chamber expanded (as you would expect), and that contacted the edge of the paddle and held it in place so it would not drop back. A few hours later, the paddle would come loose enough from the heat chamber cooling and drop back under spring pressure. Also, the little vibration from just driving the rig would allow the paddle to drop back under spring tension.
We like to never figured this out (changed control board and went through entire diagnostic logic chart). Finally, I found out that simply banging on the furnace case with the heel of my hand immediately got it running. From there it was an easy fix.... just a mater of bending the paddle over about 1/32 of an inch. It has worked fine ever since.
... and by the way, this was a brand new unit. The RV dealer ran it before we bought the RV, but never ran it through a second cycle, so to him, it appeared fine.
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That is some serious cause and corrective action!
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2020 Coachmen Leprechaun 270QB (COA Member)
Jeep Wrangler toad for the dirt
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