vaillant problem, hot water for a few seconds

[andy33]

I'm not getting any hot water from my bath tap.
I've got a vaillant turbo max plus combi boiler. The tap runs hot for a few seconds then goes cold then hot again and so on. The central heating works fine at the moment tho.

Any ideas to fix the problem?

 

[ChrisR]

Boiler is unable to regulate the temp of the lower flow through your bath tap, due to sludge in the tap water heat exchanger. Pro tem you might get a hot bath - eventually - by opening another hot tap a little, to increase flow through boiler.