Worcester Bosch Boiler Pressure

[TJ1]

My Worcester Bosch boiler pressure was set at 1.5 bar. When the heating is on it goes up to nearly 3 bars. I drained some water off and for a day or so it stayed steady at 2 bars when the heating was on.
Now it is up to 3 again when the heating is on and drops to just under 2 when off.
Has anyone any ideas please?

 

[45yearsagasman]

You may well have no pre-charge pressure in your expansion vessel.Boiler model would help.

 

[TJ1]

My boiler is a Worcester Bosch Greenstar 28i Junior. Hope this helps.

 

[andy162]

As stated, most likely an expansion vessel issue.

To test it the boiler needs to be isolated & drained. Then you would use a pressure guage that's compatible with a schrader valve( same as a car).
It should specify in the boiler literature what pressure you should find but typically it's 1bar. If it's empty then use a bike pump to increase the pressure to the specified level. Whilst doing this the boiler is still isolated & the boiler drain open, with each "pump" expect a splash of water out of the drain valve. As a (very) rough rule of thumb I find about 200 pumps gets 1bar into the expansion vessel.

Then nip up the drain valve, flow & return back on(CH circuit) & re pressurise.

It's worth pressing the schrader before you start. If water comes out, the vessel itself has failed.