Dometic Thermostat E1 Code [Causes + Fix]

The Dometic Thermostat E1 Code is an error code that generally indicates communications problems between the Dometic AC system and its sensors and (or) circuit control board.

Typically the dometic AC system is designed to communicate with its 3 main components named below:

1. Front temp sensor  that is located in the thermostat unit itself and Front AC

2. Between the Front AC and Rear AC control boards

3. Rear temp sensor and Rear AC

Possible causes for the Dometic thermostat E1 error code

As mentioned above, the  E1 on Dometic thermostat can be caused by communication problems between the AC and its sensors and the control board. In turn, these  communication problems can be caused by the following issues.

Issues	Main Fix
Faulty Thermostat	Reset thermostat
Loose Connectors between thermostat and AC unit	Unplug and securely attach connectors
Dirty Connectors between thermostat and AC	Clean and reattach connectors
High temperatures	Hold a bag of ice  up to the thermostat ( strange but works)
Malfunctioning control board	Replace control board unit.

Important: Before you start troubleshooting

Make sure that you disconnect the power by turning off the circuit breaker. If possible, engage the battery disconnect switch.

Also read:  Nest Thermostat Wiring and Diagrams

1)Faulty thermostat

Before you go any further in your troubleshooting  the E1 code, make sure that you rule out a faulty thermostat. Many times, the code can be caused by a faulty thermostat and in some cases, it could just be a thermostat that needs a reset. 

Here is how to rule out a faulty thermostat:

If the thermostat unit is registering at least one zone and that you can control that zone from the thermostat, the problem is likely not with the thermostat or the RJ11 plug connecting to the thermostat and no further troubleshooting is needed on the thermostat.

The fix

If the unit can’t register any Zones, the problem could be with the main  RJ11 from the thermostat or faulty  thermostat itself. Inspect the main connector cable and if there is no problem with it check your thermostat for possible replacement

2) High temperatures

One of the most common reasons for the Dometic thermostat e1 code is the high surrounding temperatures. When temperatures go beyond 100F, it’s not uncommon for the thermostat to fail to communicate with the circuit control board or other sensors of your thermostat. This also causes the E1 code to display.

The fix

A weird fix to this problem is to hold up blocks of ice to the thermostat and wait for the temp to cool a little bit. This will usually  start the AC and the Code error should disappear. This is a solution I was given by Dometic support and  I was surprised to see that it worked pretty well.

3) Dirty connectors between thermostat and AC.

If you have used  RV AC  for quite some time without service or a thorough clean, it could be the best time to do so. 

According to the manual, when the E1 code  keeps displaying on a thermostat, it just means that there are connection issues between your thermostat and other components and this could be caused by dirty connectors.

The fix

To start, unplug all RJ11 terminal plugs and inspect them for any dirt or debris. Clean the plugs as needed, and then reinsert them into their respective sockets. 

In a dual AC ducted system, there are two RJ11 plugs at each AC unit control board, labeled “P1” and “P2” on the schematic.

It is important to both visually inspect and clean each RJ11 plug to ensure that it is free of corrosion and loose wires. To clean the plugs, use an aerosol CRC electronic cleaner or something similar. After cleaning the plugs, reinitialize the  thermostat by following these steps:

Step 1. Turn the thermostat OFF.

Step 2. Hold down the “Zone” and “Mode” buttons simultaneously until the zones register. 

Note: you will need to turn the battery disconnect switch back on for this step, but you do not need to turn the AC breakers on.

Step 3: If the problem is resolved, both zones will register simultaneously. If only one zone registers, the problem has not been resolved and you should continue troubleshooting.

Note: you do not need to continue holding down the buttons after the zones have registered.

4) Malfunctioning control board

If the cables and plugs are functioning properly, the issue may be with the Dometic AC control board. Check the control board for any issues and consider replacing it if necessary.

. The circuit control board of the  AC is like the brain of the AC. It processes and relays signals from other thermostat to the other components of the AC system.

 When this part of AC is defective, it will cut communication from the thermostat and that could be giving the e1 code.

To access the control board, you will need to go to the roof using a ladder. Follow these steps:

1. Once on the roof, remove the plastic AC cover by unscrewing the four screws.
2.  Locate and remove the AC control board cover, which is located on the front right side of each AC unit and is held in place by two hex screws. 

Depending on your dexterity, it may be easier to “free” the control board from its corner mounts instead of trying to wiggle the RJ11 plugs with the control board in place.

Read also: How to reset dometic thermostat

The fix

A defective malfunctioning control board could be caused by a blown fuse on the circuit control board. If you can , check if the 5 AMP fuse on the circuit board has continuity.if not replace the fuse. 

You can also try swapping between the rear and the front ac control board.

Otherwise if the fuse seems not to be the problem then replacing the circuit control board is the last option. But be careful. Consult professional advice on this. 

Final thoughts

Now that you have learnt what causes  the e1 code on a Dometic thermostat. We hope that you have fixed it. If not, we encourage you to seek professionals for help.