Puma 80 problems?

Can you help me please ?


I have a problem with my Potterton Puma 80 combi-boiler. ( permanent pilot model )

When I use it for hot water only ( with central heating switched-off ), the boiler works just fine. No problems of any kind.


But.....


When I switch the central heating on, two types of problems occur :-

1. If the central heating stays on for more than 2 hours continously ( at night for example ), the system pressure gradually climbs-up from 1 Bar to 3 Bars and above, which causes the pressure release valve to open, and this in turn drops the system pressure right down to Zero Bars, which in turn turns-off the boiler due to low system pressure. If I then top-up the pressure back to 1 Bar and switch the central heating back on, the above cycle repeats itself on and on.... Basically when I'm using the central heating, the system pressure refuses to stabilise itself within its normal parameters, i.e. between 1 Bar and 2 Bars.

2. the second problem, which also occurs only when the central heating is switched on, is if I run the hot water continously for more than 10 minutes, the pilot light goes out. If I turn it back on, once again, after running the hot water for more tham 10 minutes, the pilot light goes out, and so on.....

Both problems only occur during the winter months when I'm using the central heating.

In the summer months, when only hot water is being used, neither one of these problems occur. The boiler works perfectly then.

I have replaced the electronic boards, but it didn't help.