CH pressure drops when turned off, but?

[klassickoi]

Hi.
I have a problem with pressure.
When Central Heating is working, Pressure is ok, heating is working ok, hot water is ok. When heating is turned off, pressure drops, and obviously no hot water. Turn heating back on, pressure rises, hot water works. any ideas?.

 

[Boilerman2]

Very limited info given - what boiler ? Combi? conventional?

however sounds like you have a problem with the Expansion vessel

 

[klassickoi]

Hi sorry about limited info: Glowworm Swift flow 75 Combi Boiler.

 

[muggles]

How much pressure change? You'll often get a bit as the pump kicks in and out...

 

[klassickoi]

Hi, 1.5 bar to zero

 

[muggles]

Try topping the system up to 1.5 bar when it's cold. Does the hot water work now? Turn the heating on and watch the pressure as the system heats up. What happens?

 

[xr4x4]

Also make sure filing loop is off and disconnected.

 

[klassickoi]

Hi , top up when cold to 1.5bar. Hot water works, pressure rises and expels through pressure relief valve. and holds at approx 2.0bar. Heating and Hot Water continue to work until CH turned off then pressure drops. Turn CH back on and pressure rises to approx 1.5bar hot water works.

 

[andytw]

Sounds like you need to check the expansion vessel.

andytw

 

[biscuit77]

X 2 expansion vessel