Combi Boiler Pressure

[Coogie]

Hello,

Should the pressure on a combi boiler be the same whether it is running or not?

Thanks

 

[dal5band]

They are pretty steady - that's the whole point of the expansion vessel in the boiler - it takes up the expansion hence keeps the pressure steady.
Don't know how it actually works - springs or rubber diaphram or such like.

 

[BoilerWoe]

a slight increase in the pressure when the boiler is operating as it warms up (e.g from 1 to 1.5 bar) is nothing to worry about - other than that the pressure should remain the same

 

[Soggy_weetabix]

Seems perfectly normal.

Diaphragm allows pressure to be absorbed as long as vessel is correctly pressurised.

Rule of thumb...1 - 1.5 bar cold should rise to no more than 2 bar when system at highest temperature.

David

 

[gazthepottertonengineer]

They are pretty steady - that's the whole point of the expansion vessel in the boiler - it takes up the expansion hence keeps the pressure steady.
Don't know how it actually works - springs or rubber diaphram or such like.

Diaphram

on some makes of boiler you do notice the pressure rising to 2.5 bar especially if there are alot of radiators on the circuit

 

[bripl]

on some makes of boiler you do notice the pressure rising to 2.5 bar especially if there are alot of radiators on the circuit
thats because the plonkers that fit them do not know how to size the ev and rely on the one in the boiler to cope with the amount of expansion hence some boilers get a poor name for reliabilty due to poorly trained installers/service engineers

 

[gazthepottertonengineer]

Agreed

 

[Coogie]

OK thanks. The problem is that i'm currently loosing about 1 - 2bar pressure per day, with no visible leakage anywhere. Last night went to bed with 2 bar pressure - got up this morning and it's zero!

It's gradually been getting worse over time.

OK - daft question - but does the pressure drop have to be a result is a loss of water, or can it be a loss of air. There is one radiator upstairs that i am constantly having to bleed?

British gas are coming Tuesday, but i dont want to get fobbed off.

Baxi Combi 105e with 10 rads - Thanks

Nick.

 

[bripl]

the expansion vessel on a 105e can take a sys volume of 125litres after that you need to fit an additional vessel, have you checked outside at the safety discharge pipe if it is not going outside you have a leak on the sys in the house.if you are venting the rad then you need to replenish the water in the sys.rhs of boiler is the s/v pipe it should terminate outside tie a plastic bag over the end of the pipe if it fills with water thats the leak if it stays dry it is inside under the floor somewhere hope this helps