Honeywell 42005748 001 Wiring Centre, 24 V

Product Information

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. 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 room thermostat is shown with a neutral connection. However a 2 wire thermostat can be used which does not require a neutral. Operation - Hot water only

The valve has two plumbing connections - in and out. With no power applied, a spring holds the valve closed so no water will flow. We are currently using Royal Mail Parcelforce and DPD as our delivery providers, all small items will be delivered by Royal Mail, these can take up to three working days to reach you. 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 problemsThere is no standard for which color wire controls each function. When wiring, each wire should be identified by what terminal(s) it connects to — never by color. If you don’t know to which terminal each wire connects, it may be necessary to go to the HVAC system and look at the designations on the control board. Consult your owners/install guide for wiring examples and systems compatible with your thermostat*. 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. 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. 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 I have managed to install the reciever and get the relay working OK, and when you adjust the temperature the relay opens/closes and you see the wireless display call for heat with the flame symbol.

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 If your O or B terminal shares a label with another wire — typically W —identify whether you have a heat pump system or not. A heat pump runs your compressor for both heating and cooling. If you don’t know your system type, place this wire in the W terminal. If you have a heat pump system, put it in the O/B terminal. Other wires are shown in pale grey. Some or all of these will be live depending on which modes are selected - these are highlighted brown in the other diagrams below. As correct operation relies on the valve internals functioning properly, valve failure will result in some non-obvious situations. Heating only does not work Older systems simply have the boiler and pump connected to SL (10 in the wiring centre), with only N and E permanently connected.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. When the valve is powered and reaches the fully open position, the grey and orange wires are connected together. This is normally used to activate the boiler and pump. Overview Video This scheme uses a 3 port mid position valve. In the past this was by far the most common setup, as it only requires one valve.

Older systems simply have the boiler and pump connected to SL (8 in the wiring centre), with only N and E permanently connected. It can still be fitted today, however is not suitable for systems with more than one heating zone. 3 Port Valve Operation Locate any unconnected wire labeled W or W1. If you identified an O, B, or O/B wire connecting to the O/B terminal in the previous step and it has a separate W wire, place it into the W2 terminal. Connect the W wire to the W terminal if you don’t have a wire connected to the O/B terminal.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 If the switch in the valve fails, the orange wire will never be connected to power. This results in heating only not working at all, yet the system works fine with water only or heating and water. Radiators never heat up, regardless of other settings. 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. At the moment I have a wired stat (Servowarm) which has a 3 core and earth cable connecting to it from a Honeywell Wiring Centre. Only two of the cores and the earth are being used at both ends. (Yellow, Red and Earth) 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