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Combi pressure drop

klondike Member Posts: 1
I have a Bosch/Worcester CD28i Combi boiler that is about 7 years old. Just lately the pressure gauge is always on zero? I can recharge the system but it will soon drop to zero again.

I have checked for leaks and cannot find any. The only thing I have noticed that is different of late is a mild banging in the morning when the heating comes on. It lasts about 2-3 minutes then settles down. We've had mild noises in the past but generally it just seems to be expansion of pipes or radiators and it soon settles.

Another observation. If I put the heating on MAX then the pressure gauge will start showing 2.3 bar which seems very high to me. I usually pressurise to 1 bar but within an hour it is back to zero again.

Heating and water are both hot and working??!!

Hope someone can help please.


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Check the expansion tank...

    Toggle the Schrader valve on the bottom of the expansion tank, and if you get liquid, replace it.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Andy Byrnes
    Andy Byrnes Member Posts: 42
    edited December 2009
    Repressurise expansion vessel

    The expansion vessel is built into this boiler and can usually be found down the back. If you get your head above the boiler and look down the back you will see a red vessel with a  schrader valve like on a car tyre sticking up.

    Drain the system at a suitable drain off and leave it drained. Attach a foot pump to the schrader valve and pump to approx 1 bar.

    Once this pressure is reached remove the pump turn off the drain and refill the system and bleed.
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