Combi boiler has no pressure - do I add water to system?

30 Nov 2010
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United Kingdom
Hi everyone,

I have a combi boiler (fitted 4 years ago). It is reading 0 bar pressure when off, and that doesnt appear to change much when the boiler is firing the central heating.

I think I may need to top up the system with mains water? Also, there seem to be several valves (and a puzzle of pipes!) and I don't know how to top up properly.

I'm gonna get a plumber in for a service asap, but with the time of year this might not be for a week.

I've attached a few pictures and would be really grateful for any advice on how to top up the mains water/ restore boiler pressure.

Many thanks



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There is a valve right next to the pressure gauge at the other end of the silver braided hose , its got a black plastic handle, open the valve and you will hear the water and see the gauge move after a few seconds, make sure you turn it off when the reading is 1 bar.
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Just to be pedantic, but I should add, that isn't a combi, it's looks like a 'System' boiler, with internal pump etc.

Keep an eye on the pressure reading, if it rises quite high when the system is running, then drops down to zero again when the boiler is off, and you keep having to add water, then you have another issue that needs looking at.
Just to be pedantic 2 ... if the pressure isn't rising high when the system is running but it's still losing water over time, then there's another problem you'll need to look at :whistle:
Just to be pedantic, but I should add, that isn't a combi, it's looks like a 'System' boiler, with internal pump etc.
Just to be more pedantic, if it was a System boiler it wouldnt have an external expansion vessel, Gauge and PRV , it is a heat only boiler :rolleyes:

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