If the powerhead was removed from the valve to make it easier to change the motor, it must now be re-attached to the valve. The power head cover can then be refitted and secured with the single screw. Make sure it sits squarely on the powerhead, with no wires pushing out from the sides.

Sometimes a powerhead is able to drive the valve only part way open but not far enough for the auxiliary circuit end switch to close. This valve will then not be able to tell the boiler to fire. You should be able to feel a bit of spring resistance, right at the far end (Man Open end) of the slot. In larger properties, 28mm valves may be used (the 5-wire 3-port V4073A1088 and the 6-wire 2-port V4043H1106). The 28mm V4043H1106 2-port zone valve has a6 th wire, coloured white. This white wire might not be used. In that case it should be made safe electrically. The Y Plan and S Plan names are more commonly used when other Honeywell controls are also used (programmer, room thermostat, cylinder thermostat and wiring centre).When using two 2-port valves, the control system may be known as a Sundial S Plan system or a Honeywell S Plan system. When the programmer and stat send a Live feed to the 2-port motorised brown wire, the motor drives the valve open to allow water to pass. When the valve is fully open, the end switch closes, allowing electrical current to pass from the grey wire to the orange wire and from there to the boiler Switched Live. Unless the boiler thermostat is already up to temperature, the boiler will now fire. The powerhead or actuator is the electrical section. It’s comprised of a motor and some electronic components and usually has one or more microswitches. This can cause the valve spindle to seize. It often becomes stiff to turn at first and the valve may give intermittent problems. Eventually, the spindle may become so stiff that the valve motor cannot turn it at all.

The blue wire is the Neutral, N. The green/yellow wire is the Earth wire, E. The white wire is connected to the wire from the room thermostat which calls for heating (radiators or underfloor). The grey wire is used to drive the valve to the Water Off position, in which only the heating port A is open; it closes port B. The orange wire provides a Switched Live (Switched Line) feed to run the boiler and pump. V4043H1080 is a 2 port, 1” BSP Female threaded, 6-wire, normally-closed zone valve with an auxiliary end switch The Honeywell V4073A 3-port valve has five wires. These are blue, green/yellow, white, grey and orange. Note that the grey and orange wires are used differently from the grey and orange wires of the 2-port valve! It will make it easier when re-fitting it (just remember which end the flex was connected or take a picture on your phone). The powerhead can only fit one way round onto the valve body but if space is tight that might not be obvious. The electronics in Honeywell motorised valves tend to be quite stable and show relatively few faults but the motor may fail after years of operation. Honeywell use Synchron motors and these are freely available but there are lots of cheap cloned motors out there. These look identical but, instead of the name SYNCHRON, they use the word Synchronous.

It may be easier to have the valve set in the manually open position using the manual lever. (See Honeywell Motorised Valve Manual Lever, below.)

The Honeywell valves have a D-shaped top to the spindle but you can also use a spanner on this. If you do this, you must use very little force as it is very easy to shear a spindle or damage the valve internally. If the valve motor fails, the motorised valve will not open. The valve will not then close the end switch and so will not complete the auxiliary circuit. The boiler will not fire (with no open pipe circuit to dissipate the heat), unless another motorised valve opens another pipe circuit and calls the boiler into action. This prevents the boiler firing and the pump running when there is no water circuit open. Honeywell 2-port motorised zone valves (V4043H) are electrically quite simple. The powerhead contains the motor, which is used to drive the valve open, and an auxiliary switch or end switch. Honeywell 22mm zone valve operation (V4043H1056)This can be difficult to feel for at first. It is most obvious when the valve has been in the Heating Only position and reverts to the mid-position. Honeywell V4073A1039 22mm 3-port mid-position diverter valve. These are 5-wire valves. When used with other Honeywell controls the setup is know as Y Plan Nearly all Honeywell valves have a powerhead (also called an actuator) which can be separated from the valve body. The valve body is the brass casting which is bolted into the pipework. That noise and that bump are diagnostic. They tell us that the valve has moved into the mid-position where both Heating and Hot Water ports are open. If you can make a Honeywell 3-port mid-position valve move into all three of those positions, the valve and controls appear to be wired correctly and the valve appears to be working normally. The V4043B normally open model is particularly applicable to control of solid fuel systems, since it will always fail-safe in the event of a power failure)