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Old 12-25-2018, 06:47 PM   #1
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Furnace will not turn on (2015 Thor Miramar 34.2)

The furnace stopped working during the night, but the propane showed it still had 1/3 tank. Went and filled up the tank just in case it wasn't showing correct, but the furnace still will not turn on. It is a Coleman Mach Thermostat. The fan only comes on when turned to the fan mode. Any help is appreciated.
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Old 12-25-2018, 06:54 PM   #2
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Have you checked your circuit breaker panel?
(Beyond this: I'm in over my level of expertise: good luck! )
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Old 12-25-2018, 09:25 PM   #3
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The propane fuses if fused (12 volt). The furnace fan is also 12 volt so if the fan runs you have power. There is a sail switch that tells the burner to light when the air flow through the burner is sufficient. If the sail switch moves that about all you can check, the rest of burner is propane valve, ignition and overheat thermostat; so you need a professional for that analysis.
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Old 12-25-2018, 11:30 PM   #4
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There is a reset switch just behind the outside panel, outside the motor home. You have to remove the screws, pull the panel off and it’s right behind that. This reset switch controls everything, the fan and burner, so if the fan is operating then it’s not this switch. Good luck.
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Old 12-25-2018, 11:47 PM   #5
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Furnace will not turn on

I didn't see any breakers listed for furnace, so looking like I will need to take it in. Thanks everyone for the information.
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Old 12-26-2018, 01:57 AM   #6
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When you say the FAN runs, are you talking about the AC fan of the FURNACE fan? You cannot turn the furnace fan on with the thermostat, you can only call for the furnace to deliver heat. When that happens, the furnace fan will start and begin pushing air. Once the sensing device knows that air is moving it will signal the propane valve in the furnace to open and the igniter to start sparking to ignite the propane. It will try this 3 times before it times out if it doesn't sense the burner is lit. You can reset it with the reset switch as described above, wait 30 to 60 minutes for it to time out and reset itself to try again, or turn the furnace off at the thermostat fo a minute and then turn it back on again.

Lots of Thor motorhomes have problems with the control board getting wet and interfering with the furnace operation. You can check that by removing the same outside panel that gives you access to the reset switch. The circuit board is right below it. Check the bottom of the circuit board for moisture, you can remove it with one screw.
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Old 12-26-2018, 04:41 AM   #7
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Open the outside compartment.
Check the circuit board as it has a light that will blink error codes. Many of us have had issues with water collecting on and under the control board. Even mold. Dry it off, or blow it off, reset and try again.
All of the furnace devices and the thermostat are 12V, so check for furnace fuses not breakers.
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Old 12-26-2018, 09:52 PM   #8
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There are two switches on the thermostat; the switch that has heat, cool, off, and fan is the switch that when turned to fan the fan comes on. When we have it to heat and the temp is turned up there is no fan or anything.
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Old 12-26-2018, 10:05 PM   #9
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Check the reset switch outside behind the panel where the furnace chimney is.
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Old 12-26-2018, 11:22 PM   #10
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Quote:
Originally Posted by Sholly View Post
There are two switches on the thermostat; the switch that has heat, cool, off, and fan is the switch that when turned to fan the fan comes on. When we have it to heat and the temp is turned up there is no fan or anything.
The FAN switch just controls the AC fan. Sounds like the wire from the thermostat to the furnace telling it to run is disconnected. Have you pulled your thermostat and checked Thor's fine wiring? As I recall they used small wirenuts to connect the thermostat wires to the wire runs to the furnace and AC.
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Old 12-27-2018, 02:37 AM   #11
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Hi, make sure the thermostat is switched to “heat” and turn up the temperature so there is a call for heat. The 12VDC that powers (or switches through the thermostat) typically comes through the furnace unit. If you have a thermostat with its own batteries (does not use the coach 12vdc for power) make sure the batteries are good. If you have a multimeter use the voltmeter part and see if there is 12vdc on the thermostat R or RH labelled terminal. You will probably need to carefully open the face portion of the thermostat to get at the labelled wiring terminals. If there is no 12vdc on the thermostat R or RH terminal you will need to open up the outside furnace unit door (described by previous poster) and determine where the 12vdc has failed. You should have a manual for your furnace that has a schematic.....if not search for it on line. Normally when the thermostat calls for heat the control board in the furnace will start the furnace fan motor and when it starts blowing air the sail switch operates (it's located inside the fan area in the furnace) which tells the control board that the furnace fan is working properly so the remainder of the furnace ignition sequence can continue. If the furnace fan does not run as you say, you need to look for where the 12vdc feed has failed/opened. (Fuse, breaker marked furnace, bad wire connection etc. The multimeter is an essential and inexpensive tool that every RVer should own and learn to use).
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Old 12-28-2018, 05:36 PM   #12
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Furnace will not turn on

Couldn't find a reset switch, so I tried the hair dryer. Still nothing.
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Old 12-28-2018, 07:00 PM   #13
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I have the same unit, it’s right behind the outside panel, it says reset right on the switch. It’s a rocker type switch.
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Old 01-05-2019, 07:37 PM   #14
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Furnace Control Board

We have a 2014 Miramar 34.2. Last year the furnace quit on a November camping trip. After searching through the breakers and fuses, doing a rest, the unit had to be taken to a shop. The control panel was toast. Tech thought that water may have gotten in to the unit and caused the damage. The furnace has worked fine since.
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Old 01-05-2019, 10:59 PM   #15
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My Hurricane does the same thing. The thermostat controller locks up after three failures to ignite the main burner. To reset, turn the heat control switch off, and set the thermostat to a low temperature. Wait 15 seconds, and turn the switch back to heat. It did not work with 1/3 tank in my unit, but restored use of the heater when the tank was full. I’m guessing there may be a problem with the sensor that monitors the pressure of the propane flow.
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Old 01-07-2019, 04:36 PM   #16
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Hope this helps.

I hope this helps, I recently had a similar issue. The heat would attempt to come on but after about 30 seconds it would shut down.

Turns out there is a microswitch on the furnace from the outside. It senses the airflow and then allows the propane to ignite, if it fails to activate, the furnace shuts down.

I ordered a new switch and while I was waiting I decided to take the existing microswitch out. There was some dust that prevented the switch from activating, I simply blew the dust out and reinstalled it and it worked just fine.

It was very simple and a free fix!

Good Luck!
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Old 01-12-2019, 01:44 PM   #17
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I found the reset switch, but that didn't change anything.
All fuses checked good.

It ended up being a loose connection.

Thanks everyone for your help.
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Old 01-12-2019, 01:55 PM   #18
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Well...where was the loose connection. We all want to know just in case it happens to us?

I am dealing with a bad circuit board that has been wet. I fixed it a couple of times but this time it won't work. I've ordered a new board and expect that will fix it. I have power at the board but nothing happens when heat is turned on.
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Old 01-18-2019, 07:28 PM   #19
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Sorry it took so long, but we took it to be looked at. They said it was the furnace plug. They disconnected the plug, applied some contact gel, and connected it back together. Everything works now.
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Old 01-19-2019, 03:07 AM   #20
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My board has been wet many times. I bought a replacement and that fixed it. There is supposed to be a different mounting kit to angle the board so it won't get wet so easily.
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