I'm no expert (I'm afraid) but it sounds like your partner has indeed opened the valve to top up the pressure and inadvertently created a problem. I thought all pressurised systems had a safety pressure release valve which opens at about 3 bar to avoid blowing something somewhere else in the system, so I'm slightly puzzled that this hasn't automatically reduced the pressure to 3 bar. Anyway, no matter, YOU can reduce the pressure by letting out some water either through a drain cock if you can find one or by opening up a bleed valve on a radiator and letting out water (perhaps as much as a litre?). Have your partner keep an eye on the pressure gauge and simply let water out until it is down to 2 bar, then shut it off. Do this with the system cold or you'll scald yourself!
Richard, December 2008
