Out of nowhere, after about six hours of operation, our Truma heater started reporting the error or warning W151H (water temperature exceeded in winter mode). As a result, the heating switched off until it had cooled down again in order to restart. After another six hours, the same error again.
The heater draws in cold air via a fan to keep the boiler at the desired temperature. If this air is now too warm, the error mentioned above will occur. Truma states that the solution is to open all air vents, but this was the case with us. To get to the bottom of the problem, we decided to take a look at the heating system. After a visual inspection, the culprit was easily identified….
The air hose leading into the bathroom had come loose and the Truma was heating itself the whole time. Of course, the air could not be cold enough for cooling.
Quickly put the hose back in the right place and the error no longer occurred. A typical case of small cause, big effect.
