Help on how to "Pump Up Expansion Vessel"

[Zip]

Hi

Tony from this group helped me regards on how to re pressurise expansion vessel via FAQ's.

The FAQ took me so far, but did not explain one point.

FAQ states: it's "imperative that water or air is allowed to escape from the heating system"

MY QUESTION
Does this mean while I'm pumping I get someone to 'hold open' the PRV (sort of half way?) like on the cusp OR does it mean that something else has to be open while pumping up?

Cheers, Stephen

Below is from the FAQ


4.6) During this phase it is imperative that water or air is allowed to escape from the heating system as it is pumped out of the Pressure Vessel. Otherwise the system pressure will resist your pumping and give a meaningless reading. If you aren't sure, let some more water out of the system when you have the air pressure at the right level. If that makes the air pressure drop, pump a bit more and release water and so on, until it doesn't.

 

[B&Qsuck]

Do exactly what is says in your extract... Pressurise the expansion vessel to the MI's, then drain some water from the system (Via DOC) if the pressure in your expansion vessel remains the same as you just set it to, job done!

 

[Soggy_weetabix]

MY QUESTION
Does this mean while I'm pumping I get someone to 'hold open' the PRV (sort of half way?) like on the cusp OR does it mean that something else has to be open while pumping up?

NO. You risk damaging the PRV.

Open a drain cock or remove a bleed screw from a rad (once pressure released)

The expansion vessel must have no pressure in it when you re-pressurise, and when you pump the air into it, the displaced water will need to go somewhere (ie somewhere outside the heating system)

David