High boiler pressure

[vladmeero]

Last year changed all plumbing in the flat, new boiler, pipes, rads etc. Since, the boiler pressure is above 3 both when on and off. When release water from rads the pressure falls but usually goes back above 3 over night. Checked mains valve - not leaking. Corgy guy looked at boiler, said its fine... Does anyone know what might be the cause and how to solve it?

thank you in advance

[Steviegb]

Sounds to me like your filling loop on your boiler is passing, can`t be anyhing else, providing its all piped up ok.If it only goes up when you use it , it could be your expansion vessel thats gone, but if it goes up on its own when there is no use from it, mains water is entering the system causing the pressure to rise. You will probably find the pressure relief pipe outside is dripping as well.

[vladmeero]

the pipe outside is leaking, untill i let some water out of the rad. Is it possible that plumber connected one of the mains pipes to the close circuit system? If so, can it be checked without pulling the floor boards up?

[Steviegb]

Does your boiler have an external or internal filling loop? Extrnal one will have a flexible silver hose conected from a 15mm pipe(cold water) to a 22mm pipe(return to boiler). If it has make sure the tap conected to the flexi pipe is turned off and slowly disconect it. If when you start to pull it away, water starts squirting out you know thats where your problem lies. You could always try turning your water off over night.(drop your pressure to about 1bar first). If it hasn`t risen then you know that mains water is entering the system.

[vladmeero]

the valve is external. Does not leak. I guess water is coming in from somewhere else. Might it be that when plumbing got redone, plumber crossed heating pipes with mains ones?

p.s. thank you for all the answers, very helpful