Tony-I took apart the PCB assembly to get at the switch, worried it a bit and applied some WD40. Got it clicking like a good 'un in response to the water pressure, and re-assembled. All seems OK..fingers crossed! :D
Many thanks for your help..Dave J
I have a Potterton 80 combi boiler which has always had the problem with the hot water still heating (red LED on the PCB on) though all the taps are off-quickly opening and closing a tap would do the trick. Now the problem has worsened with the LED on all the time- have had to put the boiler on...