Low pressure at shower after running for approximately one minute

[graham.g.clifford]

I have a sealed heating system, with hot water supplied from storage cylind= er, which is 30months old. in the last 2 months the pressure at the shower = head reduces after about a minute. The low pressure is preceeded by a noise= which sounds like air escaping.=20

Can anyone help please. What may be the causes of this?

[Roger Mills]

which is 30months old. in the last 2 months the pressure at the shower head reduces after about a minute. The low pressure is preceeded by a noise which sounds like air escaping.

You have a restriction in your mains cold water supply, stopping it from keeping up with demand.

Somewhere in the system - most likely on the cold inlet to the hot cylinder - you will have a pressure vessel which will store a small amount of water either at mains pressure or at whatever pressure the upstream regulator is set to (typically 3.6 bar) - whichever is less.

When you open a hot tap/shower, the demand will initially be satisfied from this high pressure store. Unless mains water can flow in at the same rate as water is flowing out, this store will be exhausted and the flow rate at the hot tap/shower will be reduced.

Make sure that your stop tap where the mains enters your house is fully turned on, and likewise any stop tap out in the street. If that doesn't cure it, suspect your pressure regulating valve.

[harryagain]

Yes, exactly so.