Your new thermostat may not be directly compatible if you see terminals labeled A B C, or 1 2 3, as your system requires a communicating thermostat. The valve is not powered at all, and the spring holds it in position B, so water from the boiler only flows to the hot water cylinder. As programmer terminal 1 has power, so does wiring centre terminal 7 which is connected to the valve grey wire. The white wire already has power via the room thermostat, and as power is applied to both grey and white, the valve moves to position A. Due to several seconds being required for the valve to move from B to A, there is a delay between selecting heating at the programmer and the boiler starting. Possible problems This scheme uses separate two-port valves, one for hot water and another for heating. It can be easily extended to include additional heating zones by adding an extra valve and room thermostat for each zone - this is typically called S Plan Plus.

If the valve motor fails, the valve will remain at position B and hot water will never reach the radiators. Radiators and hot water always work together Older systems simply have the boiler and pump connected to SL (10 in the wiring centre), with only N and E permanently connected. Power starts at terminal 3 (HW On) in the programmer. This passes via the wiring centre terminal 6 to the cylinder thermostat. If heat is required, power continues to terminal 8 in the wiring centre, and on to the boiler and pump. Identify any wires labeled R, RH, or RC. You typically have one or two of those three. If you have one wire — even if it’s labeled RC — it goes into the R terminal, setting the jumper connecting terminals R and RC in place. Thermostats may have a jumper switch, metal staple, or plug. The jumper may also be a wire connecting the two terminals. If you have two wires, R or RH go into the R terminal and RC into the RC terminal. If you have more than one wire (for example, you have a wire labeled R and another wire labeled Rc), remove any jumpers between the R and Rc terminals or push the switch to open the RC terminal to insert a wire.so far i have connected everything apart from the cylinder stat, I was going to use the old switchmaster one that was there but this has different wires and i cannot find any info on it to determine which is which so i will buy a new one tomorrow and fit this in the wiring center shortly Once the valve is fully open, a switch inside connects the grey and orange wires together. Since grey is permanently connected to power, the orange wire provides power to terminal 10 in the wiring centre, and from there to the boiler and pump. Operation - Hot water and central heating These diagrams show a modern boiler where the boiler requires mains power all the time, with a separate wire used to activate the boiler and the pump connected directly to the boiler. Unlke the Y-plan system, operation of hot water and heating are totally separate, and this layout can easily be extended to support additional heating zones simply by adding an extra valve and thermostat for each zone. It can also be adapted for use with underfloor heating. Operation - Hot water

Referring to your photo, remove and label each wire. If a terminal has multiple designations like W and O/B, it will be labeled as W and O/B and not just one or the other. This diagram shows the wiring layout using the most typical components. Here, coloured wires indicate the permanent mains supply to the boiler and programmer. The coloured valve wires are also shown. You should typically see an 18-gauge solid core wire. The most common configuration is five wires. However, you could see as few as two and many as ten.If you see wires connected to terminals labeled G1 G2 G3, you need a thermostat capable of controlling multiple fan speeds; none of our retail thermostats are compatible with this system type. G is compatible, but not G1, G2, or G3. The boiler and pump are switched via the valve. Therefore problems with the valve will mean the boiler never switches on, or in some cases will run continuously.

On most valves, the actuator head containing the switches and motor can be replaced as a separate unit without draining the system. On some, the internal motor can be replaced, although it is often easier to change the whole head. As correct operation relies on the valve internals functioning properly, valve failure will result in some non-obvious situations. Heating only does not work As with hot water only, the orange valve wire is connected to power via the wiring centre terminal 8, but orange is still not connected to anything inside the valve. Operation - Heating only This results in a noticeable delay when switching on heating only, as the motor has to move the valve from B to A. This takes several seconds. Overview Video

2 Port Valve

These systems contain a wireless controller with a wired receiver unit. The receiver unit replaces the existing programmer. The wireless controller contains a room thermostat and is used to control both the heating and hot water, so any existing wired room thermostat must be removed.

I have bought a Honeywell sundial wiring centre to help me out which is pretty self explanatory as far as the connections are concerned.This video covers the wiring and electrical operation of an S plan system with two 2-port valves. Wiring diagrams and further information continues below. View on Youtube. System Wiring Older systems simply have the boiler and pump connected to SL (8 in the wiring centre), with only N and E permanently connected. Here, power is also applied to programmer terminal 4, which connects via wiring centre terminal 4 to the room thermostat. If heat is required, power continues to terminal 5 in the wiring centre, and therefore to the white valve wire. It can still be fitted today, however is not suitable for systems with more than one heating zone. 3 Port Valve Operation Note that although the orange valve wire is connected to power, this does nothing, as orange is only connected via an internal switch when the valve is in position A. Operation - Hot water and central heating