Caling Gas fitters/plumbers/general clever sods. We have a basic boiler and thermostat at home, and we want to replace it with something more advanced than the 24 hour timer fitter to the boiler itself. I have three wires coming in, how do I know which they are and will I ruin the boiler if I get it wrong?

You will need to disconnect the timer on the boiler and replace it. You shluld be able to get a wiring diagramme to let you know what is possible