Alpha cb25 pressure drop problem

[mordzy]

Hi,

We are having a problem with our Alpha hecb25 boiler.

It seems to work fine untill we turn up the central heating thermostat on the actuall boiler (to make the radiators hotter)

When we do this the pressure drops and the low pressure warning light comes on. to fix this we allow more water into the CH circuit using the one valve from the mains to top it up

to only way to prevent a pressure loss it to leave the thermostat on number 4. anything above seems to create a pressure loss.

Can anyone help?

A plumber has been round and checked for pipe work leaks (inside, round the radiator valves and joints etc.)

Thanks

 

[mordzy]

*Bump*

can anyone help?

ta