The motor in the valve has failed ( but why doesn't the manual open cause flow and the boiler to fire up ? ) Sometimes turning off the HW allows the CH to work, after some minor gurgling noises from the system Occasionally we come across a Honeywell motorised valve where the powerhead jams but the spindle (actuator shaft) is still free. Where this happens it is usually with the valve jammed open. If all the power to the central heating system is turned off, and the manual lever is still loose across the whole slot, the mechanism may be jammed.

With modern boilers, the boiler sends a Live feed to the circulating pump which then pumps heated boiler water through the valve. It will go to the radiators or to the cylinder coil, depending on which valve was opened. With older boilers, the Live from the auxiliary circuit end switch goes directly to the pump at the same time as it goes to the boiler Switched Live. A normally-open valve is open when no power is being applied to it and needs electrical power to drive it closed. The auxiliary circuit allows several 2-port motorised valves to be used to control separate zones without interacting electrically. Otherwise, if several zone valves were used without auxiliary circuits, and all were connected to the same pump so that the Live wire that opened each valve also fed the pump Live, there would be problems. We find it is normally about 2.1kΩ (2100 ohms) if the motor is cold and up to 2.4kΩ (2400 ohms) if the motor is quite warm. I think that a reading anywhere between 2.0kΩ (2000 ohms) and 2.5kΩ (2500 ohms) suggests that the motor windings are probably OK. If the reading is many times higher than that, or it is open circuit, the motor has failed. 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.If I move the lever to manual open position, nothing happens, neither CH or HW pipes from valve become hot and boiler does not fire. Does this suggest that the valve mechanism is not opening? 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 With the powerhead cover removed you also have access to the screw which retains the motor. The motor can, if necessary, be removed without disconnecting the powerhead from the valve body. Seized motorised valve spindle in an old Satchwell Sunvic 2-port motorised valve. The water leakage has caused white oxides to form round the brass spindle, making it too stiff to turn

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. Honeywell make a large range of motorised valves used in domestic central heating systems. The most common by far are the 22mm 3-port, 5-wire, mid-position valve and the 22mm 2-port, 5-wire, zone valve. These 22mm valves (3-port V4073A1039 and 2-port V4043H1056) are used in smaller and medium sized properties. Synchron valve motors can remain energised and hot for many hours a day, all through the winter. They may eventually fail. A failed Synchron valve motor will prevent a 2-port motorised valve from working. The valve won’t be driven open and the end switch will not be made (connected) so power will not be sent on to the boiler or pump. 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. When using two 2-port valves, the control system may be known as a Sundial S Plan system or a Honeywell S Plan system.

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Whereas the internal electrics of the 2-port valve are quite simple, the internal electrical controls of the V4073A mid-position valve are more complex.

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. Only when both white and grey wires are energised (and the valve goes to the Heating Only position) can the orange wire get its 230V supply via the valve itself. (Remember, the orange wire can also get 230V from the cylinder stat if it is calling and a hot water program is on.) When all electrical power to the heating controls is switched off, the spring pulls the ball across to close port A, leaving port B open. This is the relaxed state or de-energised state of the valve. It is also sometimes called the Normal state. 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.If the powerhead (actuator) can be safely removed from the valve body (see warning above about pre-1985 Honeywell valves) you can try to turn the spindle. You may need a tool unless you have strong fingers. You must also isolate the electrical supply before removing a Honeywell motorised valve powerhead. I have yet to establish if the valve head ( the bit with the motor ) can be removed without having to drain the system. Apparently it is dependent on having a later model of the Honeywell valve. Two screws hold on the motor to the valve in the later models, and two others hold the plate to the valve body. The Honeywell mid-position motorised valve has three ports in a T configuration. Water enters via port AB. Water leaves by either port A or port B or by both at the same time. Port A is normally connected to the radiator circuit and Port B to the cylinder coil (to heat hot water). The circulating pump is usually connected to feed water from the boiler into port AB. 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.