The diverter valve is a component unique to combi boilers. Its job is to switch the flow of heated water between the central heating circuit and the domestic hot water (DHW) plate heat exchanger when a hot tap is opened.
Symptoms of Diverter Valve Failure
No hot water, heating works normally: The diverter valve is stuck in the heating position and cannot switch to domestic hot water mode.
No heating, hot water works normally: The opposite — the valve is stuck in the domestic hot water position. Radiators remain cold.
Intermittent — alternating between fault states: The actuator motor is failing but has not seized completely. This is the early warning stage that precedes complete failure.
Diverter Valve vs Actuator Motor
The diverter valve assembly consists of two main parts: the valve body (the internal flow-routing component) and the actuator motor (the small electric motor that rotates the valve to the required position).
Actuator motors fail more frequently than valve bodies. Before replacing the complete valve assembly, it’s worth testing the actuator motor independently — if the motor is the failed component, replacing only the motor is significantly cheaper.
Actuator motors are typically replaceable without draining the system, reducing labour time. Call our helpline to discuss which part is most likely based on your symptoms.
Installation Notes
Diverter valve replacement requires the system to be de-pressurised and the valve circuit isolated before work begins. This is a Gas Safe engineer job.
After fitting a new diverter valve:
- Re-pressurise and test for leaks before firing the boiler
- Confirm the valve switches correctly between CH and DHW mode
- Test domestic hot water output temperature and flow rate
- Check the central heating circuit returns to correct operation
Need a Recommended Installer?
- HGB Heating Kent — Gas Safe engineers, Kent and Medway
- Boiler Sense — Certified boiler specialists, Kent and South East London