zoned system, pressure drops when cold (but goes back to normal when i manually open valve)

[Paul Cochrane]

Hi all!

Sorry if this has been asked before but i haven't been able to find anything out there...

We made our CH system zoned when I laid some UFH in the kitchen. (2 zones total: kitchen + rest of house) each zone has a Honeywell 2-port zone valve. The boiler is a Glowworm combi.

All is well with the system *except* when the heating isnt running and the system cools down. When this happens the pressure drops. HOWEVER if manually open one pf the honeywells the pressure instantly is fixed and returns to the normal 1.0 bar. For this reason I'mm 99% certain there isn't a leak in the system (pipes were all replaced 18 months ago)

I recently installed an auto-bypass valve thinking that this was the culprit. However, no matter what setting i change that to, the problem remains.

Any help greatly appreciated, if you need any further info do ask!

Cheers,
Paul

 

[Scott_D]

Any pictures?
Did you add an addition expansion vessel?
Is there a ufh manifold?

 

[Paul Cochrane]

Hi Scott, thanks for your reply!

No I didn't add an expansion vessel, but yes there is a manifold for the UFH. Have added some pictures (it's still a work in progress as you can see! Sparky will sort cabling when he does 2nd fix)

Thanks,
Paul

 

[Paul Cochrane]

Sorry @scott_d photo upload option doesnt appear to be working on mobile, will upload from laptop in a mo.

Thanks,
P

 

[Paul Cochrane]

Hi @scott_d here are the pics I mentioned earlier. the combi boiler is just above, out of shot, if you need any more info do just ask, thanks again!

Paul

 

[Scott_D]

Wow, what a mess!

How many rads and how big is the ufh?
What model of GW combi is it?

 

[Scott_D]

Have you cut the PRV pipe?

 

[Paul Cochrane]

Yeah I know! I think a pro may be called in to put in some copper to neaten everything up, but in an effort to minimise exlense I've installed the UFH myself (also found it v difficult to actually get quotes for installation: no-one seemed to want to do it)

The UFH is a single run of 50metres. There are 7 rads in the house and the boiler is a Glowworm Easicom 24...

Thanks again,
Paul

 

[Paul Cochrane]

...re: PRV pipe... Yes, that's gonna be replaced!

 

[Scott_D]

Yeah I know! I think a pro may be called in to put in some copper to neaten everything up

Don’t call the guy who did the rest of the copper!

If the PRV goes its going to soak the electrics!

 

[Riley]

Which it might with no expansion vessel. I suspect no one wanted to fit it after you’ve begun. Nothing worse than picking up a job halfway through

 

[Paul Cochrane]

Hi @scott_d @Riley just following up this thread again... So do you think the expansion vessel in the combi itself has died, or does the system now need a second EV because I've turned it into a zoned system? I'll have a look and see if there's any pressure in the internal expansion vessel if you think that's a good idea.

Will have time to fix that PRV today too!

Thanks
P

 

[Harvest Fields]

Do not do that if the vessel is inside the boiler casing. You will need a gas safe registered engineer.

 

[Paul Cochrane]

@Harvest Fields cheers! I won't touch it then...

 

[Scott_D]

It’s probably undersized now you have increased the system size

 

[Paul Cochrane]

Thanks @scott_d !

 

[SJB060685]

If system volume has increased then a larger expansion vessel must be calculated for and installed to accommodate the larger volume. If an expansion vessel is too small, lost some charge, lost all charge or charged too much then you should expect PRV discharge and as said above this dripping on any electrics can cause problems.