Hot water problem with 280 RSF combi boiler

[jetski]

I have a Worcester 280RSf combi boiler - the central heating work fine but the problem is with hot water. After turning of tap the burner stops but almost every time the over temp switch trips. It does reset when the system cools down. When the burner stops , it sounds like the water is boiling and the pressure gauge fluctuates before the h.t. switch trips.
I can stop it happening if I turn the tap on and off a few times (starting and stopping the burner)
Recently had the vent valve replaced as it was leaking - engineer never found anything else wrong.
Any suggestions?

 

[bellairaphon]

is the fan and pump shutting off straight away too? or can u hear feel them working after uve shut off the tap?

 

[jetski]

The fan and pump both stop after the tap is switched off. If the temp trip doesn't cut out - normally the pump restarts for a period then stops. If the central heating is on - they both stop for a few seconds then pump/fan restart and burner relights. Obviously when the overtemp switch trips everything stops. -

Peter

 

[bengasman]

Did this start suddenly?
Have there been any other problems at all?
Has the boiler been serviced in the not too distant past?

 

[jetski]

It did start suddenly -everything was working ok before
No other problems apart from this - central heating works fine . Hot water problem more noticeable if system is hot from central heating or large demand on hot water e.g. running a bath
Boiler not serviced recently