Combi boiler - timeswitch problem?


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?
Thanks.
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Remove the programmer and see if the boiler still fires up.
Adam
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