Y
Yorkshire Jim
I agree that some sparkys can wire up a heating system with confidence, but you do get those that forget everything and totally lose it as soon as they see SL! I too have used relays for wiring up larger systems, and once you've done a couple it's quite easy. It's all about understanding what the components do (i.e. Where they switch, etc.). With the modern boilers it's wise to have an idea about electrics so that components such as thermistors, for example can be tested. It's same with any trade, you get those that know and those that should stay at home.