You should be able to feel a bit of spring resistance, right at the far end (Man Open end) of the slot. Both of these genuine SYNCHRON motors work in Honeywell motorised valves. The motors SYNCHRON make specifically for Honeywell come with two blue wires 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. Slide the blunt end of the motor sideways until the flange comes out from the tab holding it down. This can be a bit of a fiddle. The motor then comes free of the valve, held only by the two wires which connect it electrically. These two wires may be blue (in a Honeywell original Synchron motor) or orange (most replacement Synchron motors). When a demand comes from the programmer (via the thermostat), the motor is energised and drives the valve open to allow water to pass. When the valve is fully open, a microswitch is operated in the powerhead, connecting the grey wire to the orange wire. This is called closing the switch. It sounds a bit counter-intuitive, but when a switch is closed it is completing the circuit and allowing current to pass; when the switch is opened it is opening a break in the circuit and stops current from passing.

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.

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Honeywell V4073A1039 22mm 3-port mid-position motorised valve showing inlet port AB and outlet ports A and B. This valve can be open to either port A or port B, or to both ports at the same time Much of what we describe also applies to ACL Drayton motorised valves like the Drayton 2-port ZA5/679-2 22mm zone valve and the Drayton 3-port MA1/679 22mm mid-position valve. Iflo motorised valves and British Gas motorised valves have similar faults. It may also apply to the Tower VAL222MV motorised valve, the Siemens CZV222 motorised valve and the Flomasta 27900SX motorised valve. The Honeywell V4073A is a spring-return valve. Port A or port B can be closed by a rubber ball, though never both at the same time. The rubber ball is moved between ports A and B by an actuator shaft or spindle which is driven by the powerhead. The inlet port AB can never be closed; the ball only moves between port A and port B. 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 using a 3-port valve, the control system may be known as a Sundial Y Plan system or a Honeywell Y Plan system.

In normal operation, with a heat-only boiler, central heating water is heated in the boiler and then pumped round the system by a circulating pump. Motorised valves are used to split or divert the flow. The heated water can either be sent to the radiators (or underfloor heating) or to the cylinder coil to heat the domestic hot tap water. The cooled circulating water is then returned to the boiler to be heated again. 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. If, for example, the heating valve is failing in this way, you will get heat round the radiators while the cylinder hot water is being heated too. When the cylinder is up to temperature, the hot water motorised valve closes and no longer tells the boiler to fire, so the heating now stops too. If Hot Water is then satisfied (either by the programmer or cylinder stat), the grey wire is energised. As there is still a demand for Heating, the valve will motor to the Heating Only position (port A open; port B closed) and switch a 230V supply onto the orange wire, to power the boiler. 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).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 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. 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. If you know how to work safely with mains voltage electricity, the valve motor can be tested with a multimeter. With the mains electrical supply turned off and isolated, the resistance across the two motor wires (either both blue or both orange) can be tested. To test correctly, at least one of the two motor wires must be disconnected from the heating wiring circuit.

In smaller properties there is usually one programmer which has two channels. One programmer channel controls the heating (radiators or underfloor) and the other programmer channel controls hot water. Where additional zone valves are used there will usually be another programmer or timer. Honeywell motorised valve construction As with most equipment, parts or tools, there are a few things you need to consider before buying a motorised valve, including ensuring that your heating system can use motorised valves.

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The rubber ball sits against the circular port (right side in photo), closing it off. We’re told that the ball touches one edge of the circular port first, causing the ball to rotate slightly on its spindle. This regular slight rotation evens out distortions in the ball. A little piece of elegant design work by Honeywell! 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. System boilers may also have a diverter valve or zone valve built into them and might not have any external zone valves. V4043H1056 is a 2 port, 22mm compression, 5-wire, normally-closed zone valve with an auxiliary end switch