Expansion vessel.

[lofty531135]

Hi.
I have a problem with my expansion vessel as the system pressure keeps rising and keeps blowing the pressure reief valve,I have read if I depress the valve in the top of the expansion vessel and water comes out then it means the vessel is broken.

What I would like to know is if the expansion vessel is faulty can I fit an external larger capacity vessel of 12 litres,I have an 8 litre vessel at the minute,the reason being is I have 8 rads with one of the rads being a large double.

If it is ok to fit a larger capacity vessel would I need to upgrade the pressure relief valve from 3 bar to 6 bar to which the maximum pressure of the new vessel would be.

Thanks in advance.
Lofty.

[JimH]

Lofty - check your top up valve isn't open?

[Blake]

As above first. If not first decide if it is the EV by isolating the boiler, draining and then checking the pressure in the EV.

If you fitted a new EV, you do not need to upgrade the PRV, the boiler needs it to be a 3 bar for safety reasons.

[Puddle]

Never every increase the pressure release valve 3 bar activation point for the system it is designed for, the pressure release valve does not have a 3 bar release just for the protection of the expansion vessel, it is for the protection of boiler and all of the system and also you should never be near a units or parts maximum pressure, you may well find the expansion vessel fitted now ,also has a 6 bar max pressure or greater

To think about putting on a 6 Bar replacement p/r valve is a very dangerous thing to do and could cause serious injury to someone

You can fit another ,bigger expansion vessel externally near the boiler, the bigger size ,in fact will decrease the expansion within the system, thus system pressure when hot, so in theory ,you could decrease the p/r activation point

Back to problem, is the system pressure going up when system cold or when system being heated/hot, you may just need to just pump up/re prime existing expansion vessel to 1 bar,if pressure increasing when heated or if increasing when cold you have another problem

[mikegas]

I was told that as a temp fix for a faulty expansion vessel you can drop the system and vent all rads except 1 and this rad will act as an expansion vessel, can anybody tell me if this would work?

[quality]

Yes it will but it is only a temp measure and it must be a large radiator

[lofty531135]

Thanks for the replies.

What happened was when the boiler was heating,the prv was dribbling,so I changed the prv (3 bar) and the same thing happened later on that day with the new prv fitted,the reason I noticed was that the system pressure fell from 1 bar to .8 of a bar,so I topped the system up to 1 bar and switched the boiler on to heating and the new prv started dribbling again when it was at the set tempreture.

The system pressure gauge does not show bar when it is on heating.

I was going to test the pressure in the Ev,I have to buy a pressure gauge,it needs to be .5 of a bar,by top up valve do you mean the valve on top of the Ev,the cap is on the valve.

If I close the flow and return on the heating and open the drain cock will it empty the Ev.



I wouldn't have uprated the prv without asking as I know they are fitted for safety reasons.

Thanks.
Lofty.

[wheeto]

Hi.,I have read if I depress the valve in the top of the expansion vessel and water comes out then it means the vessel is broken.

To answer your question, yes that sounds like the diaphragm in the EV has failed. As others have said, a larger EV will be fine and leave PRV at original setting.

[spanner]

yep would work lowest radwell!!!!!!!!!!!

[gas man]

I was told that as a temp fix for a faulty expansion vessel you can drop the system and vent all rads except 1 and this rad will act as an expansion vessel, can anybody tell me if this would work?

yes this will work on a large rad as a temp measure