E4 error on Dometic thermostat

[kiralynn]

Hey everyone! I am living full time in my Montana 3790RD RV up in Wisconsin and have had quite a few issues with my Dometic thermostat. It is flashing an E4 error, my furnace will not kick on and this time of year it is chilly to say the least. It flashed this error for a while but my furnace was still working so I didn’t think it was anything to be too concerned about until I woke up this morning to my furnace no longer kicking on. I have checked my fuses, breaker box, took the faceplate off to make sure no wires came loose and have done a hard reset and still nothing is working. Does my thermostat just need to be replaced? Any information would be super helpful, thank you!

 

[DutchmenSport]

This off the internet:

Dometic Thermostat E4 Error Code indicates an open circuit or out-of-range outdoor temperature sensor on select models. This error typically affects heat pump and dehumidification functions, but the air conditioner, furnace, heat strips, and fan should continue to operate normally.

Common Causes and Fixes:​

• Loose or damaged wiring: Check the two-wire connector on the outdoor temperature sensor (located on the condenser fins inside the rooftop AC unit). Ensure it is securely plugged in. Reconnecting it can resolve the issue.
• Faulty outdoor temperature sensor: If the sensor is defective, it may need replacement. Some users report success by temporarily placing the thermostat in a freezer for 10–30 minutes to reset it.
• Control board failure: On models without a heat pump (especially those with a manufacturer number starting with 64), the E4 code may point to a faulty main control board (Part Number: 3313107.076). This is a known issue in some 2015–2017 models.
• Incorrect thermostat settings: Ensure the system is not set to heat pump mode in temperatures below 40°F, as the heat pump will lock out and trigger the E4 code.
• Loose internal electrical connections: Inspect the wiring inside the RV near the thermostat (behind the filter cover). Loose connections, especially those using household wire nuts, can cause intermittent errors. Replace with proper crimp connectors and electrical tape.

 

[DutchmenSport]

We recently had an E1 error code on ours. According to the internet, that was a "communication error." It was COLD and WET outside, no way was I going on the roof to open up the air conditioner.

I attempted tracing all possible errors to no avail. Then a thought hit me. Maybe the problem was the thermostat itself. We have 2 thermostats, one in the middle kitchen area for the front living room AC / heat pump / furnace, and a second for the rear bedroom AC. It was the front AC / heat pump / furnace one that was erroring.

Simple test? I simply switched the 2 thermostats. And guess what? The front one, now in the rear was still erroring out, only now on the rear AC only unit.

The one originally in the rear, now on the AC / heat pump / furnace position worked just fine. I was able to get the furnace running and heat going again. We did not need the AC in the bed room, so the one functioned just fine.

Meanwhile, we went to Amazon and ordered another thermostat (actually 2 of them). If one failed, more than likely the second one will fail soon also. So while we were "there", just go ahead and get 2 of them.

It took about 2 days for the to be delivered. I swapped out the broken one (in the bedroom) with the brand new one, and whall-A! It worked beautiful.

We now have the extra one in my arsenal of RV parts waiting to fail box.

My suggestion: If you have 2 thermostats in your camper, swap them and see if the error occurs on the other location. If it does, it's the thermostat itself that's gone bad. No reason to mess around with anything else, just get a new thermostat.