We have a Vaillant boiler VCW-sine 18T3W and a Randall timeswitch 103E.
The boiler is set for both central heating and domestic hot water.
The boiler and timeswitch were both working fine, but suddenly - with all
hot water taps turned off and the central heating not timed to come on, the
boiler came on and continued to operate.
There was power to the timeswitch, but switching the timeswitch to 'off' had
no effect - the boiler continued to stay on.
In order to stop the boiler, we switched off the central heating using the
switch on the boiler.
Even with the timeswitch 'off', if the central heating switch is switched
on, the boiler comes on.
Does this mean that the timeswitch is faulty and must be replaced?