Unvented H/W system - shower losing pressure

[fatboy b]

Not me, but a guy in the office. We've established, despite sketchy details, that he has an unvented H/W system.

Shower works fine initially, then loses pressure after a few minutes. Seems an "air gap" needs to be restablished (googled prblems on unvented systems)?? Is this likely, or something else needs looking at.

Ta.

[Brother D]

Unvented is dependent primarily on two things; Incoming pressure and bore size.

Seems strange pressure would drop after a while? An initial burst of water followed by a slowing down (bore size small, pressure high). But a gradual reduction in flow rate? Are they definately using unvented? and are they in a shared house?

[fatboy b]

Has no C/W tank, and a pressure-vessel above the H/W tank. Family of 4 in the house.

[Arthur Jackson]

Has it always been like this or just started? It sounds like a 'poor flow' issue. If it has a pressure vessel it doesn't have an 'air bubble', which wouldn't cause this anyway.
If it's always been like it then it's likely to be a mains flow issue...and a badly spec'd system. If it's just started then I'd look at a blockage in the main.

[andy43]

Is he half-cocked?
Sorry, is his stop cock half closed?
Just sounds like poor incoming flow - cylinder is keeping the flow and pressure up initially, then the mains supply can't replenish it fast enough.

[fatboy b]

andy43 said:

Is he half-cocked?
Sorry, is his stop cock half closed?
Just sounds like poor incoming flow - cylinder is keeping the flow and pressure up initially, then the mains supply can't replenish it fast enough.

That was my thought. I've told him to go and check all valves that should be open are open. He did say when it happened first time the pressure gauge was low. This was fixed (unsure how) and now the pressure is OK each time it happens. Doesn't affect other hot-water running btw - only the shower.

Edited by fatboy b on Wednesday 27th April 18:56