W255H in CP Plus display or no more symbols in display after reset

You see the warning message “W255H” on your CP plus display and cannot control your heating anymore?
This primarily indicates a connection problem between the CP plus and the heating. In this state, commands entered cannot be transmitted or cannot be transmitted correctly.

Attention!
A reset is not used to delete an error, but corresponds to an initialisation, i.e. a device search.
If the reset is carried out while there is a connection problem to the heating, the heating menu is completely lost. Only the time and the setup symbol remain.

Two factors can be considered as causes of the connection problem:

  1. 12 V power supply

Communication is only possible if the heater is powered in addition to the control unit. If this is not the case, the CP plus responds with the message W255H.
Please check the heating fuse in your electrical block as well as the fuse on the control board of the heating (Combi) or in the supply line (Varioheat). Replace a defective fuse if necessary.

Note: In our installation instructions, we recommend installing our units on permanent plus.
This means that the power supply to our units cannot be switched off by the central control element (main panel). There should be a permanent connection via the electrical block to the body battery.

  1. TIN connection cable

The TIN cable is used to transmit commands from the control panel to the heater. If this connection is interrupted, the CP plus responds with the message W255H.
Please check whether the plug of the TIN cable is correctly seated in the socket on both the control element and the control board of the heater.


As soon as the cause is eliminated, the warning message disappears automatically from the display.

Combi D – Tips for avoiding sooting

There are ways to protect the burner of the Combi Diesel from soiling and sooting.

In contrast to the Combi Gas, which burns almost residue-free, residues can form and settle on the Combi Diesel during use. This happens mainly in part-load operation.

Part-load operation means a permanently low power level that is mainly used to maintain the temperature.

The reason for the formation of residues is the low combustion chamber temperature that exists in 2kW operation. Unburnt fuel from diesel injection is then deposited as soot particles on the components of the combustion chamber.

The next time the engine is started, this residue burns off. You can see this by the smoke developing on the outside of the chimney. If the Combi D runs only at partial load over a long period of time, coking can occur on the components of the combustion chamber –> the heating system stops working.

This can be compared to the short-distance operation of a diesel car. If the engine does not heat up properly, this is also harmful in the long run.

Just as you drive a diesel car on the motorway to burn out the engine, with the Combi D it is also necessary to keep the combustion chamber active for a longer period.

You can achieve this by setting the hot water heating to Hot/60°C. As soon as you see on the control panel that the temperature has been reached, drain the hot water completely from the boiler. Cold water flows in and the heating system is forced to restart the burner immediately. Repeat this procedure until an hour has passed.

Tip: The water does not have to be poured away. Just collect it, let it cool down and then fill it back into the freshwater tank 😉

If the heater is only needed for a holiday trip of 2 weeks, please carry out the procedure at the end of the holiday. If the heater is used more or less often, simply adjust the interval accordingly.

New update for the Truma App (4.9.3) and Truma iNet Box (2.09.00)

  • We have added a few new features to the Truma LevelControl functions in the app. You can now easily initiate a new measurement. The result is also now shown together with the time of the measurement.
  • Alde heater owners can now activate / deactivate automatic climate control via SMS if they have a Truma air conditioning system installed.
  • We also have good news for all Combi D users:
    The “255H” and “164 H” bugs (continuous sending of SMS) have been fixed with this update and the heater can once again be used without restrictions.

Good2know:

This is how you can see what the status of the system is or whether an update is pending.

  1. open the Truma App – Settings – “iNet Box Update”
  2. at the bottom you will see the version information
  3. after the current update, these are:

Truma App version = current state of your app
iNet Box FW = Firmware version of your iNetBox
Server = available firmware version (update) on the Truma server
Local = firmware version, you have downloaded

If you have any questions or feedback, please use the comment function.
We look forward to exchanging ideas with you.