Potterton Performa 28i Fails After Using Hot Water

[ian2009]

When I run the boiler with the selector switch set to CH+HW, initially the CH works as expected, the temperature stays in the 40-50deg range, the CH green neon constantly illuminated, all rads hot (as expected). The CH will work like this so long as hot water is not used. Then I turn a hot water tap ON and (as expected) the HW green neon illuminates, and hot water is delivered correctly, - the flame amber neon also constantly illuminated (as expected).

The problem is that when I turn the HW tap off, the flame amber neon and the green HW neon remain illuminated, the temperature neons show the temperure quickly rises to 80deg then the boiler flame neon and burner turns off. The boiler remains in this state until the temperature eventually drops after many minutes, then the burner starts up and shuts down again when the temp reaches 80deg. This repeats. I have to turn the boiler selector switch to OFF (maybe wait?) then back to CH+HW to get the central heating working again.

When I run the boiler with the selector switch set to HW only, there are no problems.

Generally the fan never seems to stop even with burner off but maybe this is normal?

[The Potterton Performa 28i combi was installed in 2001.

I last had the boiler serviced by a professional in Feb 2009 and I mentioned this problem but it was not diagnosed (no parts changed).]

Any help appreciated so that I can look forward to a hassle-free Winter.
Thanks,
Ian.

 

[powell30]

Sounds like its not switching over from HW to heating......diverter valve

 

[mickyg]

Some of the detail in your info is slightly odd, but reading between the lines it sounds like your diverter valve is sticking on. Don't see what turning on and off will change mind you, only giving more time for the diverter to spring back, so it may be a slight red herring. I may be missing something... more will be along shortly

 

[Baxi-Remeha]

boiler is sticking in hw mode, need an rgi to check presure diff and micro switch are not sticking.

 

[baxpoti]

Replace prt no. 248734 differential valve dhw

You'll need the two washers as well. prt no. 248735

 

[ian2009]

I got rgi to replace the DHW differential valve, he also checked/pressurised the expansion vessel and all is now working fine.

Thanks for all of your help.