Rising Boiler Pressure - Worcester Bosch 28CDi

9 Jun 2008
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United Kingdom

Boiler - Worcester Bosch 28 CDi

The pressure keeps rising slowly from 1 bar to above 2 bar.

The central heating is switched off.

The pressure rises over a period of time - not just when the system is being used.

I recently changed a leaking pressure release valve.

Any ideas?

I assume its either :

Dodgy expansion vessel

Water leaking into the central heating circuit from cold water inlet.


Pete G
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Maybe as you said your filling loop is 'letting by' Remove it and check.

Maybe not the expansion vessel as you say the pressure rise happens when the boiler is at rest.

Could also be a pinhole in the secondary plate heat exchanger allowing cold mains water to mix with the heating side.
Maybe as you said your filling loop is 'letting by' Remove it and check.

Do you leave the 'Key' in the integral filling loop?? or do you remove after filling??

If left in, remove and see it water comes out of RHS of filling loop.

If removed then has to be pinholed H/E.

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