Gas furnace issues

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Well-known member
Jun 3, 2009
Down in S. Texas and this cold snap has required use of gas furnace as roof heat pumps could not keep up with cold temps. Have some issues would appreciate your input on.

First night we woke up with mh 54 degrees. The heatpump running and gas furnace not running. I changed tstat setting to gas and gas furnace came on and slowly warmed mh. When tstat satisfied at 68 degrees furnace shut down but would not restart when interior temp dropped. I had to cycle tstst off and back on and furnace again came on.

I have tried the gas furnace a couple times since and occasionally it will cycle normally once or twice but then require cycling off to work.

So 2 issues as I see it.
1. Gas furnace not coming on when heatpump not able to maintain temp.
2. Gas furnace not cycling properly to maintain temp.

Could this all be the thermostat?  Unit under warranty but no dealer within 100 miles so trying to see what the experts out there think.

It sure sounds like the thermostat to me. Try cleaning the switch contacts by moving it back and forth several times. Also check all the connections on the back of the thermostat to make sure they are all tight.
You might also check the spark gap at the furnace or the porcelain on  thermistor might be cracked, both will cause intermittent starts.
I pulled the tstat but could not disconnect, the pigtail that is made on the tstat was long enough that it went too far into the one place panel to reach the connector that it plugs in to. I could see the connector but could not reach it without removing the entire one place panel which I did not have time to do.
I did flex and check wiring to tstat and cycled the tstat switch several times. Will check operation with next cold front but I doubt I accomplished anything.
Any other thoughts, let me know,
I can't tell you what's wrong with it.  But ours since new has done the same thing.  The dealer has looked at it several times, sometimes saying no problem found and other times saying I think we have it fixed.  They have also swapped out the thermostat.  But it's 2 years out of warranty now and still does the same thing.  I guess dumb on my part but I've learned to live with it.  I hope you have better luck. 
Whether or not the heat pumps works along with the furnace depends on the model of the thermostat, some do and some don't, at least with those using the RPC Coleman models with the basement air and heat pump. The interaction between the electric heat (heat pump), and furnace is quite complex but is well described in the Coleman thermostat booklet available on the Coleman RPC web site (if yours is using those models of equipment).....
It could also be the zone controller, assuming you have  the furnace that  is supposed to auto-start if the heat pump cannot keep up (not all installations are set up that way). If yours is, the zone controller (mounted in/near the a/c) is what actually passes the signal to the furnace, whether from the heat pump or from the t-stat in direct heat mode.

What  thermostat model, and what heat pump and furnace?

The LP furnace is a Suburban SHD-2542, the roof airs/heat pumps are Coleman 49023-879 units and the thermostat has a name on the front RVComfor.ZC, I could not find a model number on it or on the motorhome documentation other than this.

The motorhome documentation states the LP furnace will automatically come on if the heat pumps cannot maintain within 5 degrees of the set point or if the outside temp goes below 36 degrees. Both of these scenarios has happened and the LP Furnace did not come on under either situation. Does this sound like a thermostat issue?

I called Airxcel and talked to Eric, very helpful, He had me do a couple troubleshooting checks and determined it appears to indeed be the thermostat. He is sending me one under warranty that should be here in a couple days.
He said they have had some issues with the Suburban furnaces not responding to the thermostat call for heat but that does not seem to be my issue.
So I should know in a couple days if the new thermostat resolves my issue.
We have that same thermostat and furnace controller and ours was wired wrong at installation at Thor, creating a similar issue to yours. It took an Aquahot technician five minutes to determine which wires were wrong and get it back going while he was on the phone with the controller maker's tech support.

My beef was there was no way any of that was tested at the factory before delivery or it would have been discovered.

Good luck with your solution.
Even if they don't test all systems at the factory, it should have been picked up at the dealer during the PDI.
"The LP furnace is a Suburban SHD-2542, the roof airs/heat pumps are Coleman 49023-879 units and the thermostat has a name on the front RVComfor.ZC, I could not find a model number on it or on the motorhome documentation other than this."

I have only one heatpump/ac on the roof and a Suburban LP furnace.  My thermostat says RVComfort.HP (a Coleman Mack).  Do you have 2 heatpumps/ac or just one?  It seems like you could have a RVComfor.ZC zone control vice the HP.  If you have 2 heatpumps/ac then you most likely need the ZC vice HP.  Have you always owned this RV has the thermostat been replaced before?  Not sure if this helps just my 2 cents worth.
Bought the Motorhome new earlier this year. This was the first time the LP furnace was needed since we bought the unit. I had turned it on just to make sure it worked and it appeared to work, but does not cycle properly. Unless it had been left on for a while there would not be a way to know it was malfunctioning.
The thermostat is indeed the ZC, zone control as I have 2 heatpumps but a single LP furnace. The thermostat will control up to 4 AC/Heat Pumps and at least 2 LP Furnaces. The Zone 2 heat circuit in the thermostat appears to be working as it goes to 12 V when the thermostat needs to turn on the LP Furnace when on Electric Heat, but the Furnace being only a single unit is on Zone 1 Heat and this does not work. Otherwise the thermostat seems to be working.
I could probably rewire the furnace to work from Zone 2 thermostat circuit but since it is under warranty they are sending me a new thermostat which should be plug and play - hopefully!
Thanks for your thoughts,
Checked the furnace operation over the weekend on a cooler morning to see if it might work when the tstat turned up over 5 degrees above current temp. I did not expect anything but the heatpump but the LP furnace fired up as it is suppose to do. Tried it again this morning and as long as I turn up zone 1 greater than 5 degrees the LP furnace is now firing up. It does not turn on the LP furnace with zone 2. If anyone else has this setup, is this how yours functions?

I received the new thermostat yesterday but wonder what is going on, since it appears to be working normally at the moment. I have to pull the One Place panel as I cannot reach the tstat connector through the tstat hole behind the tstat. So wondering if it is worth the effort since it is now working.

Do not know about cold weather operation as it has not been cold enough lately, so that aspect of the operation I cannot determine.
Do you have one heat pump, or two? One furnace, or two? It makes a difference to the controller.

I don't believe that controller will span one furnace across two zones, if that is in fact what you are asking.

Mine has three heat pumps, and two furnaces. Zone 1 and Zone 3 have a heat pump and furnace each and both will function as your Zone 1 now does. My Zone 2 is a heat pump only.

I know, it's complicated.  8)
Two heat pump/ac units and one 2 speed lp furnace. Appears when on electric heat the lp furnace is only tied to zone 1 for backup when the heat pump cannot maintain temp.
Have not figured out how the low or high speed is activated on the lp furnace. The owners manual does not say.
Ours works the same way, two heatpump zones but LP only backups on 1 zone.. Only the front zone thermostat has GAS on the switches.
Have fixed your furnace yet?  I had the same symptoms. I found  that when this happened, the house battery reading on the one place was down below 12 volts.  I was hooked to shore power, so my  80 amp converter should have easily handled the load. I found a loose nut on the 80 amp fuse where the converter and battery cable connect (on the right hand wall of the battery compartment).  I tightened the nut and the furnace now cycles on and off as it should.
I hope this info is useful to someone.
Installed the new thermostat 2 days ago and furnace worked as expected the first night, with LP furnace cycling. Last nigh it worked until this morning when it repeated the running until temperature reaching set point, shutting down and then not coming back on until I cycled the thermostat cool/off/heat switch.
So now I am puzzled, the battery indicator on the one place indicates the batteries are fully charged, we are on shore power. I doubt we have a loose connection as I think I would see a low battery indication.
Charlie, where is the converter located on our coaches. I assume it is not part of the Xantrex inverter. If it is I know where that is located. I will check connections. Did your One Place show the low battery voltage when you were having this issue?

Thanks for your thoughts,

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