3-Port Valves
Diverter Valve (two-position)
In short
A diverter valve is a three-port valve with only two positions. Water comes in at one inlet, AB, from the boiler. Its terminals: E, N, B.
If this is your home: this page is written for heating engineers, and for learners under the supervision of one. It explains how the wiring works; it is not training to do the work. In England and Wales, electrical work in a home must meet the Building Regulations (Part P), and some of it must be notified to building control or done by a registered electrician; Scotland and Northern Ireland have their own rules. For the wiring, call a registered electrician or a heating engineer competent in controls. Work inside a gas boiler is for a Gas Safe registered engineer only. If you smell gas, leave the building and call the gas emergency number: 0800 111 999 in Great Britain, 0800 002 001 in Northern Ireland.
What it is
A DIVERTER VALVE is a three-port valve with only two positions. Water comes in at one inlet, AB, from the boiler. It goes out at one of two outlets: port A to the heating, or port B to the hot water. Never both at once.
At rest, a SPRING holds it on port B, the hot water. While the brown core is live, the motor drives it over to port A, the heating. When the brown goes dead, the spring takes it back to port B.
Do not mix up the two Bs. Port B is the hot water outlet, where a pipe joins the valve. Terminal B is the screw the brown core goes on.
It is the valve of a W-PLAN system, which gives the hot water PRIORITY: the heating gets the water only while the cylinder is satisfied. It is based on the Honeywell V4044C.
It has NO end switch. In a W-Plan the thermostats fire the boiler and the pump, not the valve.
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Terminals
| Terminal | What it is for |
|---|---|
| E | Earth (E): it must be made on the valve. |
| N | Neutral (N) for the motor. The blue must go to neutral, or the head never moves. |
| B | Brown: the MOTOR. A live here drives the valve to the heating port, A. In a W-Plan it is live only while the cylinder is satisfied AND the room thermostat (stat) calls. It is the room thermostat's live, carried on through the cylinder thermostat's satisfied contact. |
What the meter reads
Live tests. On site, any reading taken with the supply on is work on or near live parts. Regulation 14 of the Electricity at Work Regulations 1989 allows it only when working dead is unreasonable, as when a fault shows only while the controls work, and only with suitable precautions: test leads made to the HSE’s guidance note GS38, fingers behind the guards. Regulation 16 allows it only for a competent person, or a learner under the supervision of one. Wiring and repairs are always done dead. In the simulator, nothing is live.
The brown (terminal B) live, and the neutral (N) there: the valve travels to port A, in a few seconds here. The heating is fed, and the hot water is shut off.
The brown dead: the spring returns the valve to port B. The hot water is fed, and the heating is shut off.
Nothing comes out of it: it has no orange and no end switch. So read the brown.
Dead, across B and N the meter reads its motor's WINDING: about 2.40 kilohms in this simulator.
Where it connects
Lessons that use it
- W-Plan: the diverter valve
Intermediate · C-Plan and W-Plan
Also in 3-port valves
Practise it in the simulator.
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