abv set for pump overun

6 Jan 2007
Reaction score
United Kingdom
hi folks,

quick one on how best to do a crude set for an ABV on my system

Have looked at previous posts this has been debated, seems to be 2 main ways to do a crude set of an ABV, which is best for me??

It's an open vented old system in a 2 bed house, no TRVs or anything, but reason I fitted an ABV is the new glowworm boiler has pump overun (old one didn't) and system also has 2 separate valves, one for HW and one for CH obviously, so they're both closed when demand is turned off but the boiler will keep the pump running for overrun after the valves are closed so the ABV needs to open just for this. Also new boiler does run fine currently on any setting of the ABV, it's just for overrun when valves are closed I need. (I think!!)

I've read -
Method 1:
with HW and CH valves closed and just pump & boiler running, close ABV fully (which = highest pressure setting, is that right?) then slowly open until flow starts (indicated by warmth of pipes before & after bypass) then turn one more turn towards open for good measure. Done

and Method 2:
opposite i guess: with CH valved open and system running normally, open ABV fully (which is lowest prssure setting, right?) then turn gradually until it stops flowing through the bypass.

Which method do you think folks for a crude set in my case?


sorry it's a standard honeywell ABV from screwfix.
(For info the old system & boiler had a system bypass gate valve which was fully closed and it all ran fine.. I've removed gate & fitted the ABV)
Sponsored Links
Which Glow-worm boiler do you have (model and size)?
Which pump do you have?
Which speed is the pump set to?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links