I think you are testing us with this question, as anyone who is aware of such things as snubber circuits would know that an immersion heater is a resistive load and not an inductive load. In the UK there are some timeswitches which can deal with a 3kW load but I do not know of a suitable electronic timer. So on my own system which has been operating a 3kW immersion heater for about 3 years without any problems or interference with other electronics, I have used a Drayton Tempus digital timeswitch operating the heater via a standard relay from Maplins, so no snubber circuit necessary in my case.