How to replace expansion vessel

5 Dec 2004
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United Kingdom
Boiler: Worcester 35CDi
Problem: gradual loss of pressure
Suspected Fault: expansion vessel

The boiler runs fine but after pressurising it loses pressure over a couple of days, and eventually settles down to about 0.5 bar. At this point the rads. dont really get hot properly, and it is noisy

The leak is not from a rad. or pipework, but it is dripping from the overflow pipe outside. Thinking it was the PRV, I replaced it but still the same problem.

Tried pumping the expansion vessel with a bike pump, and seemed ok for about half a day. Some water came out of the valve on the expansion vessel when I took the cap off. Does this mean it is broken?

So the question: is it likely to be the expansion vessel at fault, and is that an easy thing to change (I am reasonably competant at plumbing).

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Do you mean is it a simple job to remove the boiler from the wall and replace the expansion vessel? or was there something else you were considering
If you get water out of the air inlet point of the expansion vess then its duff and has to be replaced. if its the 35cdi MK1 then its very easy to change (boiler has two pumps) if its the 35cdi MK2 (1 pump ) then its a Corgi job as the gas valve has to come out and its a bit of a pig to get out.
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Thanks all. COG was right, and fortunately mine was a MK1 and it turned out to be a 20 minute job!

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