It turned out that the problem was the boiler running too long ang getting too hot.
In discussion with Grant the cheapest option was decided to be the changing of the entire countrol panel, sensors etc. All working ok now. Thanks for all your help.
It looks as if it has been over-pressurized, with the longitudinal split. It should take 7 Bar at 82 degC, so the boiler running for too long still shouldn't cause the temperature above 82degC, unless the PRV/ expansion vessel/ thermostat are defective.
It turned out that the problem was the boiler running too long ang getting too hot.
In discussion with Grant the cheapest option was decided to be the changing of the entire countrol panel, sensors etc. All working ok now. Thanks for all your help.
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