Saunier Duval Thelia 623 boiler?

Hi Tony

Please note the presure gauge on the boiler does not measure the presure of the water through your hot taps but rather the system presure in the boiler and radiators which is a differant circuit and between 1 and 2 is ie 1.5 bar is the correct presure when system cold
your problem is due to a restriction/blockage somewere in the pipework this could be a stop cock or valve not opened fully or the filter on the cold water inlet to boiler,just after isolation point is blocked
the boiler hot water operation operates on water flowing through the boiler therefore with insufficiant flow rate this boiler will not operate on hot water mode

tony
February 2008