Combi-boiler pressure query

[rjs123]

Removed a radiator today but had problems with the connection leaking and had to turn mains water off etc to stop the leak. Have now noticed that the pressure gauge on the boiler is at zero which doesn't seem right!

Could this be to do with the leak we had earlier? We're not exactly experts in this area of DIY... Can anyone advise?

We have a Worcester Greenstar; the central heating and hot water seem to still be working fine

 

[kevplumb]

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turn the taps till the pressure rises to 1 1.2 bar

 

[MANDATE]

Can't see how turning mains water off stops leak on central heating circuit.
Within a combi boiler is a heat exchanger. It is heated using the central heating water which is sealed in. The cold mains water runs through the heat exchanger and comes out hot, so the 'sealed in' water and the mains water never mix. (unless the HE is faulty)

The sealed part is normally set to about 1bar pressure when cold it should rise to about 2bar when heated. Heating the water increases its volume and extra volume enters the expansion vessel which contains 'air' pre charged to about 1bar.
When you bleed a radiator or replace one you are removing some water from the sealed side, which means you lose some or all of the pre set pressure.
The pressure is restored by use of the filling loop that connects 'mains pressure to the sealed circuit and allowing the pressure to build up to the 1bar again.
If you go over you can bleed a radiator and bring it down. If you go as far as 3bar the pressure relief valve will operate, but once open they may leak so dont let it go there

 

[rjs123]

I think we just need to re-pressurise it, or whatever the correct term is. There's a key in the front cover but we can't see where to use it?

 

[kevplumb]

look in the FAQ at the top of the forum

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