Valves
2-Port Valve
In short
2-Port Valve: Zone valve with end switch (5-wire: E/N/B/Grey/Orange). It has 5 terminals: E (Earth), N (Neutral), B (Brown), G (Grey), O (Orange).
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
Terminals
| Terminal | What it is | On an S-Plan | On a Y-Plan |
|---|---|---|---|
| E | Earth | Wiring centre terminal 3 (earth) | — |
| N | Neutral | Wiring centre terminal 2 (neutral) | — |
| B | Brown | Heating valve: Wiring centre terminal 5 (room stat call). Hot water valve: Wiring centre terminal 8 (cylinder stat call) | — |
| G | Grey | Wiring centre terminal 1 (permanent live) | — |
| O | Orange | Wiring centre terminal 10 (switched live, on to the boiler SL) | — |
How it fails
- Heating zone valve: motor failed
The valve is being told to open (230 V on brown, neutral good) but the motor does not drive. Replace the valve head.
- Hot water zone valve: motor failed
Hot water demand reaches the valve (brown live, neutral good) but it does not open: failed motor.
- Heating zone valve: end switch failed
The valve opens but its end switch never makes: grey has 230 V, orange stays dead, so the boiler gets no switched live.
- Hot water zone valve: end switch failed
Valve opens, grey live, orange dead: failed end switch, so no switched live for the boiler.
- Heating zone valve: neutral open circuit
The motor's neutral conductor is broken. Brown-to-good-neutral reads 230 V; brown-to-its-own-N reads nothing.
- Hot water valve brown landed on the wrong terminal
The valve's brown is landed on an empty terminal, one along from where the cylinder stat's call arrives.
- Cylinder stat wired to its SATISFIED terminal
The valve is fed from the stat's SATISFIED contact, so hot water is only called for when the cylinder is already hot.
Where it connects
Lessons that use it
- What is Switched Live?
Electrical Fundamentals
- Permanent Live vs Switched Live
Electrical Fundamentals
- The Programmer
Component Library
- The Room Thermostat
Component Library
- The Zone Valve (2-Port)
Component Library
- Heating Zone Valve
S-Plan Wiring
- Hot Water Zone Valve
S-Plan Wiring
- No Power to System
Fault Diagnosis
Systems it is part of
Also in valves
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