I have a problem with my Worcester Bosch Highflow 400 rsf boiler. If hot water is on, I cannot get central heating to work. The hot water has to be switched off first. Once ch is on, I can turn hw on but it does not heat up until ch is switched off. Ch will not come on with hw off. I have to turn hw on, get it to strike up, then turn ch on and hw off. Very confusing. This happens when setting manually or automatically using program timer. I called in two plunbers for quotes. One said it is a timer fault, the second that it is a PCB fault. Any assistance or advice is welcome. Thanks. Gilbert

gilbert, January 2010

I can't get my central heating to work. i.e the pump is running but there does'nt seem to be any water returning through the system from the radiators.?

Duncan, February 2012

I have a similar problem. If the CH is on we have to turn it off to get HW. However, if the CH is on but the boiler is at temperature and not firing, the HW will work.
I've changed the diverter valve which has sorted out other problems of the hot water getting too hot and tripping the limit stat (the CH circuit was interfering with the HW circuit).
I think the problem is with the PCB. There are 2 and one controls the logic of the pump and it's over run. I need to test it but I think a relay is failing to operate the pump when demanding HW in CH mode.

Arbeerich, February 2011