Zone Valves: What They Do and When They Need Replacing

What Is a Zone Valve?

A zone valve (also called a motorised valve) is an electrically controlled valve that opens and closes to direct hot water to different parts of your heating system. They're found on system boilers with hot water cylinders, where the heating and hot water circuits need to be controlled independently.

Types of Zone Valve Configuration

S-Plan (Two Zone Valves)

The most common arrangement. Two motorised valves control:

1. The heating circuit (to your radiators)

2. The hot water circuit (to your cylinder)

Each valve operates independently, so you can have heating without hot water, hot water without heating, or both together.

Y-Plan (Three-Way Diverter Valve)

Uses a single three-port valve that diverts water to either the heating circuit, the hot water circuit, or a mid-position where both receive heat simultaneously. Less flexible than S-plan but simpler and cheaper.

Combi Boilers

Combi boilers have an internal diverter valve rather than external motorised valves. When this fails, it typically causes either no hot water or no heating (the other continues to work).

Signs of a Failing Zone Valve

**Only heating OR hot water works**, but not both (or one circuit no longer works at all)

**Boiler fires up but no heat reaches radiators or cylinder**

**Valve hums continuously** but doesn't fully open or close

**Valve becomes stuck** in open or closed position (often the first sign — you may notice the heating coming on when it shouldn't)

**Leaking from the valve body** (requires immediate attention)

Can They Be Repaired?

Zone valve heads (the motorised actuator) can often be replaced without draining the system — a relatively straightforward job. The valve body itself (if corroded or cracked) requires a system drain and is more involved.

Motorised valve heads typically cost £15–£40 for parts and are quick to replace by a competent engineer.

If you suspect a zone valve problem, contact Halo Heating on 01483 676108 for a diagnosis and repair.