problem with halstead finest gold combi boiler

[avelingbarford]

I have a halstead finset gold combi boiler.

When the central heating is active the pressure shown on the pressure gauge constantly rises and keeps on rising, but when the central heating is not active the pressure reading on the gauge drops to zero.

does anyone know what this may be. suspect it may be the diverter valve?

 

[muggles]

Expansion vessel

 

[avelingbarford]

I don't understand. Why would it be the expansion vessel?

 

[Terry7556]

read the wiki/faqs on boiler problems for an explanation, top of the headings page

 

[twgas]

no air in it to take up the expansion of the water.