Why does my Bosch Worcester 24 CDi keep repressurising itself?

Just got this problem sorted at long last - a new plate heat exchanger fitted - yippee

Dan
December 2009

The pressure is going high even when i'm not at home anyway (hence the puddle from the PRV line).
The pressure does however sometimes drop as you would expect, but not necessarily because it is cooling down. I get the feeling it is just fluctuating with the cold water district mains pressure through demand.
Does this mean it is definitely the heat exchanger and not the diverter?
Can anyone explain the purpose of the diverter, how water would enter at this point causing the increasing pressure and a way of testing whether it is at fault?
Thankyou all for your advice so far....

Dan
October 2009

Almost certainly the plate heat exchanger. This can be tested by turning off the cold water supply to the boiler for a day (no hot water) sorry. If the pressure stops climbing then you know it's your heat exchanger.

M
October 2009

Thanks

Can you see it being caused by anything other than these two things?
Can you explain the purpose of the diverter works and how this would affect the pressure?
Just like to understand more before plumber comes over again.
Cheers

Dan
October 2009

yes possible split HE more likely diverter valve need replacing, routine job if you know what your doing! you may want to call worcester for advice their technicians are v good

kiteboy
October 2009

we have the same problem and so far many plumbers attempted changed pcb board and other things etc.it still goes to this flashing light mode when central heating is on. it might work few days without any probelm and it comes back. no problem when it is on only hotwater mode. any help is greatly appriciated. we have already spent quite a lot. really desperate. what i can't understand is it works fine in hw but why is it going to flashing when cental heating is on as well. please please help if any experinced the same and how they solved it.

desperate lady
October 2009