Combi boiler hot water problem

Careful_ly

I have a problem with the hot water from my Worcester 28CDi combi boiler.
Unless the taps are turned on at full power (which is causing splashing) the boiler is not firing up. If the pressure is turned down once hot water is flowing then the boiler shuts down.
We have a thermosatic shower running from the boiler and today it would only supply hot water in 45 second blasts. If it was turned off then on again more hot water could be obtained again for another 45 seconds.
Any suggestions as to what is causing this to suddenly happen, nothing has changed on any of the plumbing, everything is 6 years old.

gas4you

Could be the diaphragm perished, or maybe, from the 45 second burst statement, the plate heat exchanger blocked on the system side.

This would need removing and cleaning or replacing if it is that.

As it is a Worcester CDi, I always recommend getting Worcester in on a fixed price repair for a diaphragm, as they are a right PITA to repair.

Careful_ly

Thanks for your help, we have a contract with N Power which I was hoping I wasnt going to need to use, as I get £90 if I don't call them out to a repair, but that is probably cheaper than what it would cost to call out Worcester. Just have to hope they send someone who can repair it!!

macman

Possibly not modulating properly, so it's detecting an overheat and shutting the burner off, cooling, and then refiring?
If so a new PCB may be required.

ziggyman99

As ever I agree with Gas4you. I'd go with the diaphragm. It's the favourite and as already said, a pig to change. In fact everything on these boilers is a pig to change....
Having said that I changed a pump, PRV, AAV, expansion vessel and DHW Heat exchanger on ONE of the these and the customer still got change out £400.