Expansion vessel pressure

[Jonny brown]

Hi just thinking that an expansion vessel pressure should be just over 1 bar . What happens if it's over or under ?

 

[Madrab]

Not necessarily, it needs set in relation to the system it's protecting. Nothing really happens and it's better to have some pressure rather than not. For it to work correctly though it needs set as per the MI. As long as it's around the 0.75 - 1 bar mark though then it should be fine.

I presume we are talking about a central heating EV?

 

[Jonny brown]

Yes the central heating EV . Here's my dilemma . When my boiler was last serviced the engineer topped up the EV with some kind of bike pump .

Since the service it's been 1bar when off and 2 bar when running . 2 bar seemed a bit too high so I let some pressure out of the EV . Now it's 1 bar when cold and 1.3 when running .
Have a made a mistake in doing this ?

 

[Madrab]

When my boiler was last serviced the engineer topped up the EV with some kind of bike pump

You shouldn't be altering the pressure when the system is hot and sealed. The EV pressure would be set during the boiler service, the system is depressurised and then the EV set to the correct pressure. The air pressure in the EV will climb when the system gets warmed up, that's what it's supposed to do.

I wouldn't think that the pressure in the EV would be 1bar when cold and 2bar when hot but then you let pressure out and is now 1bar cold and 1.3bar when hot. If you let pressure out of the EV then its cold static pressure would now be lower than 1bar.