Since just before Xmas I've had an intermittent problem with my Viessmann Vitodens 200 system boiler. Basically, after heating the water cylinder at switch on it then trips when switching over to heating the house. A re-set sorts things. Most inconvenient as you wake up to a cold house. Doesn't happen every day, though. But more often than not. Can happen if you run off a lot of hot water like say for a bath, but less often than not.
The Viessmann engineer called twice under warranty and on the second visit (last Friday) replaced the main board with one which has later software. Saturday it worked fine - today back to its old tricks. The stored fault code he reckoned was a red herring (something to do with the burner).
I'll phone Viessmann technical who are very helpful on Monday and get the engineer in again - but anyone got any guesses as to a likely cause?