Expansion vessel full of water

[WhoMe?]

Nope - it filled up, because there was no air pressure in it, to prevent it filling up..

Would that have happened because the CH was off all summer?

Re-charging the vessel will force the water out of the vessel, as long as the system pressure has been released and a vent/drain is left open as the vessel is being charged up.

Any EV, whether it's large or not will fill up with water anyway when the system heats up and the water expands, that's the way it works. When the system is cold and under normal pressure, ~1bar, then the pre-charge pressure in the vessel pushes the water out of the EV and into the system, as the system runs and heats up the water expands, the pressure increases and forces water up into the vessel, as the air can be compressed, then it does absorbing that increase in pressure and stops the system from overpressurising.

If the EV is undersized, it means that the system water volume and pressure increase is greater than the vessel can absorb, the system pressure then rises to the point that the PRV may lift.

As suggested though, they should be doing it - oh and the EV pre-charge won't need to be up as high as 1.5 bar, no more than 1bar would normally be required.

Thanks, very thorough and informative. So release the pressure via a rad and leave the rad open? I assume the highest rad in the house and be prepared for some water to be pumped out of the rad as the EV is pressurised?

 

[Madrab]

I assume the highest rad in the house and be prepared for some water to be pumped out of the rad as the EV is pressurised?

Doesn't need to be, any rad or drain point will do. Again though, that shouldn't be your job, part of a proper service should be to check the EV and re-pressurise if possible, if membrane compromised then notify that the EV needs replaced.

There will always be some water in the EV but it shouldn't be able to run out through the schrader valve as that's the air/gas side of the membrane. You may get a little moisture from the valve when testing as it can gather condensation but not squirting lots of water.

 

[Johntheo5]

12 rads and underfloor heating in kitch/diner

Grant boilers have the PRV set to 2.5 bar I think so the minimum EV volume required will be ~ 16L assuming a system volume of combined rads & UFH of 175L, the installed EV will have its volume stamped/labeled on it.
A 24L EV is supplied with the 36 Pro I've just seen.

 

[WhoMe?]

Grant boilers have the PRV set to 2.5 bar I think so the minimum EV volume required will be ~ 16L assuming a system volume of combined rads & UFH of 175L, the installed EV will have its volume stamped/labeled on it.
A 24L EV is supplied with the 36 Pro I've just seen.

So for a simple person like me, are you confirming that the installed EV is large enough?

 

[WhoMe?]

Just reread, I think you are saying that, thanks

 

[Madrab]

A 24L EV for that size of system should be more than enough, if that's what the original EV was replaced with but you need to confirm that's the size of it, as suggested check the label on the vessel, that and a 24L vessel is pretty big

 

[Johntheo5]

Just reread, I think you are saying that, thanks

Yes, but just check that it actually is installed, some oil fired boilers come with a internal EV of ~ 12L volume which would be too small for 12 rads + a UFH system..

 

[WhoMe?]

Yes, it's 24L. Thanks all for the advice