Worcester 24i junior gaining pressure

[Monkeypowah]

Got the old 24i with twin pipe heat exchanger, the system is filling even with filling loop removed and drops when you run the hot, all points to a leak between water and system, but can those twin pipe exhanger do that, seems unlikely a leak would find it's way into the other circuit, without ****ing out on the floor as well?
Also the guy reports having to pressurise the system for weeks everyday till it started filling itself.
When you run the hot the pressure drops 1 bar straight away and visa-versa,
all seems a bit odd, i'll isolate mains to boiler tomorrow.

 

[nickso]

most are tube in tube design so , yes, it can happen.

 

[bengasman]

Never heard of this happening on a bi-flow.

 

[Monkeypowah]

Ok just downloaded manual and seen that they al have a built in filling loop, the guy has built the mother of all tile diy boxes around bottom of boiler and is going to dimantle it himself, thats why can't isolate mains.
But it has a filling loop under the unit that works, maybe the built in one is open? Or did they make some without internal loop?