Honeywell 42005748 001 Wiring Centre, 24 V

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This arrangement is common on new installations, as it allows for multiple heating zones with the minimum of additional plumbing and wiring. 2 Port Valve

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 The valve has two plumbing connections - in and out. With no power applied, a spring holds the valve closed so no water will flow. 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 (8 in the wiring centre), with only N and E permanently connected.There 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*. 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) 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. 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

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 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 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 onlyThis 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 This video covers the wiring and electrical operation of a Y plan system. Wiring diagrams and further information continues below. View on Youtube. System Wiring 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.

The only addition to acheive heating only is terminal 1 (HW Off) of the programmer being connected to power. To protect your equipment, turn off the power at the breaker box or switch that controls your heating and cooling. To confirm your system is off, change the temperature on your existing thermostat, so the system starts heating or cooling. If you don’t hear or feel the system turn on within 5 minutes, the power is off. You can skip this step if you have a digital thermostat with a blank display.

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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.

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. 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 It can still be fitted today, however is not suitable for systems with more than one heating zone. 3 Port Valve Operation This is simply the above two diagrams combined. Unlike the Y-plan system, operation of heating and hot water is totally separate, they do not interact or require the presence of the other. Possible problemsIf 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 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 The same result is acheived if the hot water cylinder is fully heated - the cylinder thermostat provides the 'HW Off' signal by connecting C and 2 together.