Combi boiler Pressure Build Up

[leave-it-alone-mark]

Hello All,
I have a 10 year old Combi Boiler that was having problems with pressure build up and a leaking pressure over flow pipe. This went on for some time but as the central heating has not been on for a while it had not been a major problem. Recently (after turning the central heating on and blowing the safety valve) we finally found that the cold water feed for the pressure top up inlet was leaking! This has now been disconnected and the pressure now sits at 1 bar when cold, excellent I thought!
When I now turn on the heating the pressure slowly rises but it does not stop at 2 bar or 2.5 bar which I would expect (hope), it keeps going, when it gets to about 3.5 I loose my bottle and shut it down again.
All the radiators start to get warm and they have been bled, any ideas what the problem could be? As I said, the pressure is now constant when the heating is off but it rises and keeps rising when the heating is on and I can't risk blowing the safety valve again as I have to get a "boiler man" each time to reset/replace the valve and we loose all hot water (which the wife holds me solely responsible for).

 

[corgiman]

See loads of other posts on this type of problem

Sounds like the pressure vessel to me callan engineer, although I think some las will advise topping it up yourself I would strongly recommend profession help for this

 

[oilman]

See loads of other posts on this type of problem

Sounds like the pressure vessel to me callan engineer, although I think some las will advise topping it up yourself I would strongly recommend profession help for this

I would agree with this, esp with the info in the question. BUT if you are getting a boilerman in each time the valve blows, don't get HIM in again!! He should have sorted your problem the first time. Get someone competant.

 

[leave-it-alone-mark]

Hello and thanks for the responses.
It appears I misunderstood the need for a boilerman to reset the pressure safety valve. The reason he was needed last time was because the valve was clogged with muck etc etc due to the fact that it had been leaking for months, then when the heating was put on it let go in a big way and was jammed open. It has now been cleaned and reset and works correctly, I did not realise the valve resets itself when the pressure drops.
Anyway, with this new knowledge I put the heating on again and watched the pressure reach almost 4 bar, then the pressure forced the water out of the overflow and I turned it all off again (and the valve reset itself).
Having spoken directly to the boilerman he said that it sounded like the "expansion vessel" may have had it (due to the age and also being under high pressure for so long), he suggested replacing existing one or perhaps installing a universal secondary one? Is this the same thing as the "pressure vessel" you mention?
Thanks again for your comments, Mark

 

[Gees]

Yes its the same thing. Sometimes hidden at the back of a combi and difficult to replace. You can fit an external tank. Its supposed to be on the return as near to the boiler as you can get it. You may have to seal up the valve on your original vessel. One of the metal tyre valve covers should do.. ( I think )

I am NOT a heating engineer or plumber