Central Heating Electrical Wiring - Part 2 - S Plan - YouTube Click to view on Bing19:25Electrical wiring for central heating systems. Part 2 in the series looks at S plan wiring, a system which uses two separate valves. One valve for hot water, another for heating. Support thisAuthor: John WardViews: 207K Combi Boiler with 2 heating zones | ElectriciansForums Usually the SL to the boiler from the zone valve oranges, terminates into terminal 4 at the boiler. If you can find the 's plan plus' diagram and ignore the hot water part of it, this will show you how 2 seperate heating zones are connected. wiring up a 2 zone heating system | DIYnot Forums wiring up a 2 zone heating system. Discussion in 'Plumbing and Central Heating' started by profet, We have a Worcester combi boiler that provides the hot water and central heating. Any chance of a wiring diagram to help or it is really a job for an electrician?