There are several types of motorised valve that you may come across which are used to control the flow of water in central heating and hot water systems. Typically these may include the following
Motorised Valve Types
Two-port valves which simply open or close to allow or prevent the flow of water.
Three port diverter valves which allow water to be routed to the hot water circuit or the heating circuit, but not both.
Three port mid position valves which allow water to be routed to the hot water circuit, or the heating circuit, or both.
Motorised Valve Faults – Actuator and Valve
There are several reasons why a motorised valve might fail but usually, the fault will be with the actuator assembly. This is the motor section mounted on top of the valve. If the valve has seized up or is worn and leaking then a new valve will need to be fitted. A good indication of a seized valve is when it is difficult or impossible to move the manual override lever. If the motor assembly (actuator) has failed, you will still be able to use the manual override lever. Failed actuators usually default to the hot water open position. There is an override lever on the side of the casing which can be moved from auto to manual to open the heating circuit instead.
Replacing a Faulty Actuator
The first thing to check is that there is the power to the actuator. A mains tester can be used for this. Assuming the power supply is ok and that the actuator has indeed failed, you will need to buy a replacement. To make life as easy as possible, buy an exact replacement. Nowadays, most actuators can be replaced without needing to drain down the system. On older types, this isn’t possible and you will need to drain before starting work.
Switch off the boiler then the electricity supply to it by removing the fuse from the plug or fused spur outlet. Double-check that there is no power to the terminal box for the motorised valve connection. Move the manual override lever to the manual position then remove the cover.
Under this, you will see the actuator which is held in place by two retaining screws. Undo these and cut the wires where they go into the terminal box. If you leave a small length of each wire still connected to the terminals it will make things easier when it comes to wiring up the new actuator assuming you have bought a like for like replacement. Now, remove one old wire at a time from the terminals and connect the new wires to their corresponding terminals. Position the manual override lever to manual on the new unit and gently fit it to the valve assembly. Don’t apply any force as this will damage it. Secure the new unit with the retaining screws and refit the cover.
You can now put the override lever back to auto. Refill the system if it was drained down. Reconnect the power supply and switch the boiler back on. Check the operation of the system for hot water and heating.
Replacing a Faulty Motorised Valve
If the motorised valve has seized or become worn and is leaking, a new valve will need to be fitted. It is essential that the same type of valve is fitted – diverter, mid-point, etc. Life will be a lot easier if you fit an identical replacement so that no adjustments are needed for the pipework.
Switch off the boiler and then the electricity supply to it by removing the fuse from the plug or fused spur outlet. Drain down the system. Undo the compression joints where the motorised valve is connected to the pipework. You will need to hold the body of the valve while doing this to prevent any undue force on the pipes. Obviously removing the unit on a three-port can be a little tricky. If it cannot be removed, the pipes will have to be cut and later extended to suit the new unit.
Remove the olives from the pipe ends and clean to remove debris and dirt. Olives can sometimes be eased off with the help of a wrench. If not, cut them at an angle with a junior hacksaw.
Slide the nuts for the new unit onto the pipe ends followed by the new olives. Now carefully maneuver the valve into position so that the pipe ends all sit into the outlets of the valve fully. Tighten the nut on each connection holding the valve body to prevent twisting. Wire up the new unit as detailed above and in accordance with the manufacturer’s instructions
Refill the system and inspect the work to ensure there are no leaks. Reconnect the power supply and switch on the boiler. Run the system to ensure all is operating correctly