Pressure drop when heading

[colinnic]

Thanks in advance for any responses.

Basically my central heating system is losing pressure but I cannot find any leaks. It's losing around 0.5 bar in a day. I've checked the overflow pipe and the water is not coming out of there. It's possible that the leak is under the floorboards downstairs.

The one thing I have noticed is that the pressure gauge drops by around 0.5 bar when I switch on the hot water taps or when the central heating is actually heating the water in the system. I thought the hot water was isolated from the central heating and therefore wouldn't affect the pressure? Could this be causing the loss of pressure?

I had the expansion vessel replaced a couple of years ago but I suppose the new one could be broken.

Boiler is a Vokera Linea 24.

 

[cross thread]

ex vessel may need resetting to its correct pressure,when the pump starts you get a slight negative pressure reading on the gauge

 

[colinnic]

Thanks for the very speedy reply. The new expansion vessel doesn't seem to have a method for re-pressurising unlike the original (it had a valve similar to a car tyre). The pressure drop seems a little high (I'm not a Gas Engineer) and remains constant (about 0.5 bar) until the hot water tap is turned off.