It is a contact that does not switch the live from the mains.
For instance, if you were to have your kettle on a timer so that it is boiled when you get up, the timer switch will supply 220V to the kettle,.e.g. the contact has 220V on one side and will supply it to the other side when on.
In the case of your boiled, you have to use a timer switch that simply control a relay e.g. whatever voltage is required comes from the boiler and it passed through the relay back to the boiler when timer switch is on.