De dietrich boiler reboots when heating

ThomasVDB

Hi,

We have a de dietrich MCA modulating boiler (2012), that does the floor heating for our ground floor, the conventional heating for our first floor, and the sanitary warm water.
When I activate the heating for the first floor, I see on the boiler display (and hear) that the heater flame start, and then immediatly the boiler reboots. Heating stops, the display briefly turns off and on. After a few seconds the heating resumes, but then it reboots again. It keeps doing this cycle, resulting in not heating our first floor.. It is however not the same as a 'cold boot', caused by electrically switching the boiler off and on, which has a longer boot up process.
Also the heating for our ground floor and sanitary warm water does not seem to be affected.
Anybody an idea what can cause this?