Pressurised central heating pressure changes

Bertie66

I have a pressurised central heating system with a pressure vessel What variation in pressure should I expect between when the water is cold and when it is at maximum temperature?

penrhyn

When cold the pressure should be around 1 bar, rising to around 2 when hot.(Baxi 105 figures).

Corrected.

TimBuckTeeth

penrhyn wrote: »

When cold the pressure should be around 1 bar, rising to around 4 when hot.(Baxi 105 figures).

That seems a large rise, which could be caused by low air pressure in the pressure vessel. Usually the over pressure relief valve opens at around 3 bar.

Bertie66 wrote: »

I have a pressurised central heating system with a pressure vessel What variation in pressure should I expect between when the water is cold and when it is at maximum temperature?

I would say a rise of 0.5 to 1.5 bar is normal depending on the size of the central heating system. Mine rises less than 1 bar from 1.3 bar cold.

penrhyn

Thanks you are quite correct, for some reason I thought the gauge was 0 - 10. Have corrected my post above.

Bertie66

I have been monitoring the system for 2 days and see that the pressure varies between 1.0 and 1.4 Bar from cold to hot, but overnight last-night it dropped dramatically and after running first thing and cooling down it is now, 9am, reading just 0.6 Bar.

I have 3 automatic air vents in the system, one above the pump and two in the loft of an extension, one on the flow and the other on the return. Is it one of these 3 vents that could be letting air into the system when it cools down overnight in this very cold weather? I can usually let some air out of the vent near the one at the pump and on Sunday last I had to bleed one of the rads, quite a lot of air came out.

I am pretty sure that there is not a leak in the system.

penrhyn

If you have bled a radiator you have let water out of the system, as a result the pressure will drop. When the system is cold fill the system via the filling loop to get the pressure back to 1 bar.

partan

how high is your highest auto-vent? if it's higher than 10 metres above the boiler pressure gauge, then it could let air into the system if it failed. I dont like them, we have them on my ship and are prone to failure. Might be worth raising the pressure when the boiler is cold to 1.5 bar, see what happens then. If it is the vent leaking back when the system cools, this may stop it, but if the vent is malfunctioning, i'd get rid

Bertie66

All the vents are only about 3 metres above the pressure vessel & gauge, the other one about. I will try increasing the pressure. Thanks