In medium sized or larger properties, using a combi boiler, there may be an additional zone valve external to the boiler which allows the heating to be split into two zones. 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.

On modern Honeywell valves, if the powerhead fails it can be removed from the valve body without draining down. However,be warned!With very old Honeywell motorised valves the powerhead could not be removed without draining the water first. 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 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. Autumn Statement: Workers to pay less in national insurance – but rate cuts don't offset the freezing of personal tax thresholds

Replacement Honeywell SYNCHRON motors are available but are a bit more expensive. For a long time we’ve used the standard SYNCHRON motors as replacements, with very few problems. If it’s the other way round, and the 2-port valve controlling the hot water circuit is failing, it may be less obvious. The heating circuit valve may be open for long periods telling the boiler to fire. If the hot water valve is partially open, you may not run out of hot water. 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. 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.

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.)A programmer and room thermostat (stat) are used to control heating times and room air temperatures. The programmer and room stat may be combined into a single programmable room stat. When a V4073A mid-position valve is set up in a Y-Plan configuration and Hot Water is called for, power to the boiler is provided directly from the cylinder thermostat. The valve is not energised. The Honeywell V4043H1106 28mm 2 Port Zone Valve 240V series of two port motorised valves has a wide range of flow control applications in domestic central heating systems. The V4043H normally closed models have end switches for electrical control of boiler and pump. The normally open model is particularly applicable to the control of solid fuel systems since it will always fail-safe in the event of a power failure. Key Features V4043C1156 is a 2 port, ½” BSP Female threaded, 3-wire, normally-closed zone valve but has no end switch