Servowarm Combi SE - Low pressure

[ServowarmC]

Hi all,

I have a low pressure problem with my Servowarm Combi and I'm hoping someone can help. Firstly I've no idea about plumbing but all seems to be ok with the heating. I get no water when 'Hot water only' is selected but have no problem when the heating is on. There is no pressure showing on the gauge so automatically think this is the problem.

There is a header tank in the loft and this is now full, anyone able to tell me how to get the pressure back up to normal?

Thanks
Chris

 

[ServowarmC]

Any ideas on this one? Is there a pressure switch or something similar that needs manual adjustment to get the pressure back up?