Blocked 240 calorifier

Hi,
I've got a worcester 240 which is overheating and firing the overheat stat in the hot water mode. C/H is fine and modureg, sensors and overheat stat have all checked out. The hot water flow rate is around 9L per min at around 55 degrees - which from the sevice data is fine. The C/H side was recently power flushed but has failed to solve the problem. Could the primary flow thru the calorifier be blocked ? If so does anyone have any ideas for un-blocking this or is a new one the only option ?

thanks
dave

You could try to descale it with chemicals, but it may not work and if you have never done this before you would probably be better just changing the calorifier. Not a bad job as long as you have a small wide-jawed spanner.

Thanks for the response,
When you say descale it, do you mean remove the heat exchanger from the boiler and submerge it in a bucket. When power flushing is it possible to flush this section of the circuit ?

On this type of heat exchanger you could probably fashion something to attach it to a powerflush machine I suppose, but I actually meant closing the boiler off from the CH system, introducing some chemicals and running the boiler on DHW demand, then when heat is applied the chemicals would attack and loosen the blockage (if it exists) and then you would flush them out and neutralise the acid.

Not an easy job if you're a DIY-er. Phone HRPC and see what a new calorifier would cost you. Also if you change it, make sure and ask them for the 'telescopic pipe' which adjoins the h/e and the diverter, as the bastard always leaks after work is done .!

Does it over heat while the HW is running or just after you turn a tap off?

If its just after then it prob the pump over run stat not clearing the heat out the boiler,

The calorifier on these is the white one with the coil through it if i remember so could be flushed throught quite easy id imagine if removed, but ud need a corgi man to do that as your working on the boiler,

would try the descaling idea if you in a hard water area first before getting somone to take parts out and induvidually flush them out.

Also if your not corgi registered you may find the burner pressure could be set to high causing problems with overheating on teh hw side.

Sorry never read you post full there, the stats are fine so would go for burner pressure or blocked calorifier, if it was powereflushed then the calorifier would not have been flushed unless somone opend a hot tap at the time to divert the water through it so may well just need induvidually flushed.