The black pressure water value will not move.So cannot reset the water pressure bar.

Hi, It sounds like the ball valve has seized on the filling loop. Contact a local plumber and ask for a new filling loop/valve to be installed. If it is attached directly to the boiler however you will need to contact a Gas engineer to replace the part on the boiler. Regards, John

i agree with the previous post if it is the filling loop valve on the boiler that has seized then only a gas safe guy is allowed to change it. The other question to ask yourself is why it has lost pressure and is the pressurised side for the rads not the hot water??? sounds like you should book yourself in for a boiler service with a gas safe plumber (should be done every year). badly serviced or unserviced gas appliances can kill people so I would call the person that has the qualifications to sort it and not take the risk.