My boiler has been OK except that it sometimes squeals when hot water (and more rarely cold water) is turned on while the radiators are on. Turning the radiators off at the boiler has (previously) stopped the noise. For the first time today, however, the loud squealing noise happened when I turned the radiators on (no taps running). Again, the noise goes when I turn the radiators off. Effectively, it seems I can’t have heating without an awful loud noise. Can anyone help?