I have a Vaillant boiler that is 7 years old.
Sometimes it decides not to switch off in the evening.
The thermostat says its off.
The timer says its off.
The hot water tank is always set to off because of the solar panel.
But the boiler happy burns through the night unless I switch its power off.
But not every night, just some nights.
My tame plumber cannot work it out
so I wondered if anybody on MN (particularly @pigletjohn) might know ....