Truma code 255

from the truma website....

"Warning W 255 H appears in the display of the CP plus panel – what should I do?

The heater does not have 12 Volt power supply or there is no connection between the heater and the CP plus control panel.

The power supply to the heater may have been interrupted by switching off the vehicle control panel (not the Truma heater control panel).

The control panel is used to control all other functions in the vehicle and it also switches the power supply for the consumers in your vehicle on or off.

In this case turn on the control panel in your caravan to reestablish power supply for the heater.

Once the power supply is guaranteed and the warning is still present, check the cable connection between the heater control panel and the heater."

its saying the 12v supply is missing, there is a 12v fuse under the removable cover on the Combi, this may have blown.

something like this...cmbi slow burn fuse

Hi thanks ive read all that in the book but still can't find the solution ourselves maybe need testers which we don't have problem is all caravan repair people are booked up, someone said battery but our battery is reading 13.8 and we've got spare battery that's also reading 13.8 I'm at a loss going away for 3 weeks Tuesday and have no water or heating 🤔 

You have my sympathy…I suffer intermittently with the same fault. Annoyingly it refuses to manifest itself when at the Truma agent even after 48 hours continuous running. I think it is something to do with the power supply between the control panel and Combi as wiggling wires and connectors in that circuit will sometimes (temporarily) resolve matters. I also think it might be temperature related - connection breaks down due to heat expansion, then resolves as boiler cools.. All speculative at this stage as investigations are ongoing. PB Board component also on the ‘suspect’ list.

have you checked the fuse i linked to? youll need to remove the Combi cover (where the reset button is) and you'll see two fuses....one is for the 230v side and the other is the 12v protection.

im guessing, without this you cant run off gas either?

as well as checking the Combi fuse, AND all other 12v fuses in your van, if you can scrounge a voltmeter, you could test the voltage across the fuse setting to ensure 12v is actually reaching the unit....as Bill says, the link from CP to Combi has been reported as a potential issue.

as a nice knowledable neighbourly chap/chapess to lend a hand..

Hi again thank you for speaking to me, ok weve got one of those meters, the code says its 12 volt problem? I assume, my husband has put meter on the cables on boiler and fuse these are reading fine, hes put meter on cables on truma panel these are fine one would presume if both ends are fine then there is no break in wire? We have just taken battery to halfords and reading says fine im so confused 

ues, thats a bit confusing as it suggestes the 12v power is ok, have you checked the fuse on the combi?

He put meter on and it buzzed i assume that means its OK 

ok, the only thing i can suggest (other than ringing Truma who are very helpful) is to completely power everything down....

un plug mains, disconnect (or isolate) all leisure 12v systems and wait at least 15mins....this is the time Truma have suggested for some of their other 12v related errors.

then turn on 12v. perhaps forget mains at this point and just try to get the unit powered up....then try it on gas.....if it works, bring up mains and test other power sources.

good luck.

On the control panel, what devices are listed on the display when you check the status? You should see something like C3.00.1 and H5.00.00 confirming that the control panel is ‘seeing’ the combi.

If you ring Truma, they’ll advise you to start by purchasing and fitting a replacement 12v power cable between the CP and combi. All makes good sense apart from the fact (in my case)  that the connections are on either side of the van and cable buried under the floor! Maybe your set up is easier to route the cable? It might be easier to test continuity of the cable and, if ok, remake the connections on each end. You may also want to replace the connection socket(s) on the combi. The problem with losing your icons after a reset suggests the CP isn’t seeing the Combi when you power it up after reset - tends to confirm power supply issue.