when your new boiler was installed your installer should have upgraded your hot water cylinder to a high heat recovery coil version (unless you already have one), fitted a cylinder thermostat, a room thermostat, along with your exisiting programmer and thermostatic radiator valves your system would then comply with the latest energy efficency regulations (law)ensuring full boiler interlocking.
Electiricans aren't always the greatest at wiring central heating systems to be honest as they are a specialist area, can be very complicated, you often find heating engineers are a better bet.
I'm not too hot on wiring but my father has 50 yrs of experience as a gas engineer including 35 yrs with british gas, you will find us in the Birmingham South West Yellow Pages under West Heath Gas, i think out ad is in the Gas Engineer section and also the Heating Engineer or Central Heating section. We cover the south of the city from Halesowen to Edgbaston, kings norton, kings heath, mosely etc but dont work north of the city centre.
if you ring ask for Phil Armstrong but dont mention this website cos dad wont have a clue what your talking about.