hot water and heating system ?

Lost pressure from what to where?
Should normally be at about 1.5 bar-water pressure switch will cut boiler out of operation if 0.8 bar or lower.To increase pressure you should either have a worcester filling link connecting cold water supply to boiler heating return utilising the worcester filling key!
Or else a flexible filler loop that does the same.Be aware that loss of water indicates a leak somewhere and not necessarily obvious-could be weepage through safety valve etc.Has the pressure guage increased at all from normal to high(if 3.0 bar or over safety valve will expell excess water to relieve pressure)and fall to a low pressure on cooling.Hope this helps.

chris the gas
February 2009