Furnace working on its own

[bikefever]

For the first month in our new 2014 3402 the furnace ran fine. Last night it started while the inside temperature was 77 with the thermostat set at 62. The furnace was not responsive to the thermostat and was only able to turn off via turning off propane or pulling the fuse. Fuses should not be used as switches but in this case it was getting hot inside.

Both zone AC units work fine. Appears to be isolated to the furnace only. Even with the gas off the furnace attempts to run regardless of thermostat (Dometic Comfort Control Center 2) setting for furnace. Fan setting for furnace is set to Auto.

Have a service appointment in two weeks in the meantime, any ideas?

[DQDick]

Should be someone along soon that has that model thermostat and can tell you how to reboot it. That would be the first thing to try, but my model is older so i won't lead you astray on how to do it.

[rohrmann]

This is from the manual:

When your unit was installed the appropriate dip switches on the electronic control
board were turned on to match your system configuration. Any time these settings
are changed, a system reset will need to be done before the CCC 2 thermostat will
recognize the updated selection. To do a system reset:
• Make sure the CCC 2 thermostat is in the OFF mode.
• Simultaneously press the MODE and ZONE buttons. The LCD will display
“IniT” and all available zones.
• Release the MODE and ZONE buttons.
• Press the ON/OFF button to exit system set up.

If you don't have the manual, you can download the pdf here:

http://www.dometic.com/enus/Americas...ctdataid=66938

[bikefever]

Rebooted or resetting the CCC2 thermostat made no change. The furnace comes on even with the thermostat in the off position. Appears that the thermostat and furnace are not communicating.

[Overlord]

Is the furnace making heat when it is running and running?

If not, and it is just the distribution fan that is running, it could be a propane supply problem, such as the built-in safety shutoff valve in the propane tank itself(if you opened the valve too quick), or the curbside regulator is kaput, or the supply hose restrictor doo-dad is clogged, or the main regulator is wonky.

Can you light the stove burners?

[JandC]

Since the system reboot did not make a difference, you may try taking off the outside panel and looking for an "on-off" switch. If I recall correctly my unit had this type of switch around the lower part of the furnace. Maybe you can just switch it off until service tech looks at it.

[bikefever]

Propane pressure appears to be ok, cooktop burners operate normally. This morning turned propane on, tried adjusting temp on thermostat, furnace did not start regardless of setting. Waited 30 or more minutes all of sudden it turned on and produced heat. Turned off gas and burner turned off and fan turned off after the normal cool down period.

[bikefever]

FYI - finally repaired. Wires behind the furnace were shorted providing 12v to the furnace, making the furnace run regardless of thermostat setting. This was a factory caused defect where insulation on two wires were stripped back too far causing them to make contact.

[TAKPAK]

Bikefever, you beat me to it, on my response. From what you were describing, it sounded exactly like what you found, that something was "shorting" and causing the control (T-stat) to be bypassed.

Good troubleshooting. You should go to work at an RV service shop???

[Tom Smith]

Same thing on mine. Drove me crazy untill I figured it out. Ran a new wire all the way .