reducing pressure in sealed CH system


12 Nov 2008
Reaction score
West Midlands
United Kingdom

I've got a sealed combi system powered by a ravenheat 84ET....

pressure is currently at just under 2.5 bar. For over a year the pressure has been dropping after the system all of a sudden over the last few months with the system on DHW only during the summer the pressure is at this 2.5 bar level when cold and the CH would raise the pressure close to 3 bar.

Now the CH isn't coming on, DHW is working, but i want to try and reduce the CH pressure down to 1.5 bar or thereabouts. There appears to be no airlocks in any of the rads, when i bleed the ones that have the bleed screws water comes out immediately....i also can't seem to locate a drain valve anywhere......either on any of the CH pipework or connected to any TRV.

All i can see are two drain valves in the downstairs bathroom on the Hot and Cold pipework leading to the bathroom sink.

I assuming i need to drain some pressure from the system to see if the CH can start up but without a drain valve i don't see how i can do it.

There are pressure reelase valves on the pipework of an upstairs rad.
And there's a pressure valve on pipework entering the ravenheat which we use to increase pressure into the question is if i can drain some pressure how do i go about doing it if i can't find the drain valve, and secondly if i am able to reduce pressure can i use the pressure valve close to the boiler to increase pressure to the system.....i don't see how else the ravenheat could be filled manually.

thanks in advance
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Drain water by opening a drain valve by the radiator until the pressure reaches 1 bar.

If no drain off, put a roller tray under a rad and loosen the valve slowly to let a bit out at a time. :D

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