E1 Code on Dometic Thermostat

Nothing is more annoying than coming face to face with an issue in your RV, especially if it is related to the thermostat. Once this component develops a fault, you have no choice but to leave everything else aside and start working on repairs.

That’s because losing the thermostat could mean sacrificing important features like the fan, the furnace, and the AC inside your RV. Sadly, that’s a common occurrence with Dometic thermostats.

Many users have reported an E1 error code on their LCD Dometic thermostat, regardless of whether it is a single or dual-zone model. The LCD error code pops up on the thermostat screen out of the blue and limits the component’s performance.  

We know that sounds stressful, which is why we are here to help. In the following article, you will learn how to troubleshoot and fix the E1 code on Dometic thermostat. 

What is an E1 Error Code?

The user manual that comes with your thermostat has all the information you’d need about error codes. The details are under the Special Instructions section if you want to look.

For those who don’t have the manual, it states:

  • E1: Loss of communication between the Single Zone/ Dual Zone LCD thermostat and the module board. LCD will cycle between E1 and the previous mode setting. The system will shut down.

In other words, if you see the E1 code flashing on the thermostat’s LCD, it is having problems reaching out to the circuit panel(s). The connectors attached to one end are not transmitting information to the other end, resulting in a complete system shutdown. So, no AC, furnace, or fan until you fix the malfunction.

There could be multiple reasons for this, like short wiring, corroded connectors, blown fuse, or faulty module. But to determine which one is right; you need to bring out your DIY hat and start troubleshooting the problem.    

Troubleshooting & Fixing the E1 Thermostat Error   

If the module has lost communication with the LCD thermostat, you can do one of the three things below.

1. Turn the Main Power Breaker Off and On

You know what they say, “If it isn’t working, try turning it off and on again.

This solution works on most electronic gadgets, and thermostats are no exception. Simply, look for the power breaker on your motorhome and switch it off and on. If you don’t know where the breaker is located, consult the user manual that came with your RV. 

However, if you can still see the E1 code on the thermostat, try the next solution. 

2. Reset the Fuse

While you are meddling with the power components, try locating the thermostat fuse. Once again, this would be easier if you had the user manual and knowledge about the fuse’s exact location. If you have neither, you can look for details online.

When you find the fuse, reset it by switching it to the off and then on position. The solution should work. However, if you still can’t get rid of the E1 error code, you should try following the next method.   

3. Reset the Dometic Thermostat 

Resetting the thermostat itself is your last option. Luckily, it is easy to do if you follow the steps below: 

  • Ensure the thermostat is in the OFF mode.
  • Press the MODE and ZONE buttons at once until you see ‘IniT’ on the screen.
  • Release the two buttons once you see the above message.
  • Press the thermostat power button to come back to the main menu.

The thermostat is reset and ready to use.

Note: The above solutions are best for non-technical people. If you are one of the more tech-savvy folks out there, have a go at one of the following few solutions.

Technical Solutions to the E1 Problem

There are several solutions for the E1 error code online. But none of them seem to work for everybody. Even Dometic doesn’t have the correct or definitive solution for the error code After all, there are several factors at play and the state of every person’s thermostat is different.

The only way to come close to a solution is by getting to the bottom of this issue.

Follow the detailed steps below to hopefully find the solution:

Understanding the Problem

The Dometic dual zone thermostat (CCC2) and the single zone thermostat use a series of RJ11 cables to transfer information from the thermostat to the module and from there to the AC unit. In the dual-zone system, the communication channel looks something like this:

The wires and connectors move between:

  • The front temperature sensor to the front AC unit
  • Between the front AC unit and the rear AC control module
  • Rear temperature sensor to the rear AC unit 

If there is a problem with even one of the connectors, the E1 error code could pop up. Alternatively, it could be the control board itself that fails, resulting in unwanted errors. So, if you get the E1 fault for one particular zone or one zone magically disappears from the LCD screen, you have to start working on the solution. 

Before You Begin

There is one point you need to keep in mind, before moving on further. If one zone has disappeared from the LCD, the problem does not lie with the thermostat or the RJ11 cables. The issue is with the AC unit or some other relative component. So, in such a case, there is no point in meddling with the thermostat and its settings.  

Let The Troubleshooting Begin

1. Eliminate the Possibility of Corrosion/Loose Connection in RJ11 Cables

First, turn off the main breakers, remove the RV from shore power, and disconnect the 12V battery. Once you have done that, it’s time to reach the AC’s control module. There you will find two RJ11 cables, one for the front and the other for the rear AC vents.

But to access this you would have to go on top of the RV’s roof and remove the protective cover. It is held together by four screws, so you will need a screwdriver set for assistance. Once you are there, undo the screws for the AC control board and gently yank it out to view the RJ11 cables. You would have to clean the two connectors thoroughly to have any effect on their efficiency.

Next, you must move to access the four RJ11 cables situated behind the front air intake and the four located behind the rear air intake. You would have to get down and dirty to access these connectors as they are hidden behind a metal screen.

So, in total, you would have to clean and manage 12 RJ11 connectors.     

Remember to use a good quality electronic cleaner to wipe the ends of each connector and to reinsert them properly in their slots after cleanup.

Now, reset the Dometic thermostat in the way that we described earlier in the article. Hold the Zone and Mode buttons simultaneously to reset the component and your thermostat should be good to go.

If the cleanup operation you just performed didn’t bring out the desired result, try the next step.

2. Ensure the RJ11 Cables Are Not Faulty

If the RJ11 cables connecting the front unit of the AC to the rear unit are faulty, the thermostat could also develop an E1 error code. What you will need to test this out is a crimping tool. It is used to deal with telephone wires and you can get it from your nearest hardware store.

Once you have the crimping tool in your hand, get a regular phone cable or ‘RJ’ cable and use it as your testing tool. You have to cut the end of the cord and place a connector on top but flip it over 180 degrees. So, it is inverted and not in its regular position.

After completing this task, connect the two AC modules by this one cable and test each connection one by one. If you remember, 2 RJ11 cords are running between the two boards, which means you have to try four combinations to rule out all possibilities.

If the missing zone comes back up, it means the RJ11 cables are at fault and need replacement. You can further confirm this by using an RJ11 tester (buy it at a hardware store) and using it to isolate the trouble-making cord. You only need to change the one causing all the fuss. After all, there is no point in changing all of them in one go.     

3. Swap the Front and Rear Modules

If the cables are working and you still have the E1 error, perhaps changing the position of the control boards could provide some relief. But before you begin, turn off all the power coming into your RV, to protect yourself from a mishap.

You need to access the control modules one at a time. On each board, there are eight standard-colored connectors, four multi-connectors, and two RJ11 cables. The location of each connector is important, so it is advisable to take a photo of the control module and all its connections before removing them.

Once you have removed the cords, undo the four pins holding the board in its place and swap them with the other module. Reconnect all the wires and cords and reattach the pins to hold the board in place.

We know it is a lengthy process, but this level of troubleshooting will eventually lead you to the answers you need.

So, if you can see the zone back on the LCD thermostat and the E1 error is gone, that means there is a problem with the control module. You need to replace it with a new one. If you can find it easily, try getting two, because you never know when you might need it again.

Note: (The CCC2 control boards part no. 3312022 and 3312227 are the same)

After you get the new part, replace it with the old one, and don’t forget to reset the DIP switches for the front and rear units. Reinitialize the thermostat by turning on the 12V battery power and it should be good to go. You do not need 50A shore power to restart the system, as others might suggest.

Final Thoughts

By now the E1 code on Dometic thermostat should disappear. After all, we have provided you with all the possible ways to solve the problem. From turning the system on and off to changing the control module, you should have tried every method. Hopefully, your worries go away and never return.

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