I have a Worcester Bosch Greenstar 27CDi boiler. It should be kept at
1.5 bar, but it tends to drop after a couple of weeks, and I need to
top it up again.
Is this normal please, or is there a leak?
If there is a need to top them up, then there logically must be a leak
or pressure loss somewhere. It could be that the pressure vessel is low
on air, such that as the water heats up instead of the vessel being
able to accommodate the expansion, it is blown out via the pressure
Other than that it might be a leak at a valve, TRV, or from a pipe, or
joint. These leaks can be very difficult to find, because you don't
need to actually loose much water for the pressure to go down. If you
really cannot trace it, the best way is to drain the system completely
and find some way to pressurise it with just air. Air leaks out much
more easily than water and therefore produces a noise which can be
That typically does not present as a gradual pressure loss over weeks.
It normally presents as a catastrophic pressure loss after one heat cycle.
Also easily tested by taping a plastic bag over the vent pipe to capture
The pressure relief valve inside the boiler can leak. I used to have to
top up the pressure every few months but recently it was needing it
every few days. Since the boiler is under contract I called in WB and
they replaced the PRV and now it is OK.
Mine does the same and it is the pressure relief value (waiting for it to be
replaced). Put a bag over the end of the outside outlet and see if it is
Never know, might be the same thing and an easy fix if it is.
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