The diverter valve inside a Baxi combi boiler switches the flow of heated water between the central heating circuit and the domestic hot water circuit. Baxi diverter valve failure is one of the most common fault types on Baxi 600 and 800 series combi boilers, particularly as the boiler ages beyond the 5–7 year mark.
Symptoms of Baxi Diverter Valve Failure
No hot water — heating works normally: The diverter valve is stuck in the central heating position. The boiler fires, heats the radiators, but turning on a hot tap produces cold water. This is the most common failure presentation.
No heating — hot water works normally: The valve is stuck in the domestic hot water position. Radiators remain cold.
Intermittent hot water: The valve is not seizing completely but is operating with hesitation. This is the early stage of failure — the actuator motor is weakening.
Heating and hot water both work but with reduced output: If the valve is not fully closing in either position, there may be short-circuiting between circuits, resulting in lukewarm radiators and below-temperature hot water simultaneously.
Diverter Valve Body vs Actuator Motor
The Baxi diverter valve assembly consists of two parts: the valve body and the actuator motor (the small 24V DC motor that drives the valve between positions).
In most Baxi diverter valve failures, the actuator motor is the failed component rather than the valve body itself. The actuator motor sits on top of the valve body and is replaceable without draining the system — significantly reducing labour time.
Signs the actuator motor has failed:
- Mechanical grinding or clicking when the boiler attempts to switch modes
- The motor does not turn when tested with a voltmeter confirming 24V supply
- The valve body can be moved manually (with power off) but the motor does not turn
Baxi Diverter Valve Models
Baxi 600 and 800 series use slightly different diverter valve configurations. The Baxi Platinum uses a valve assembly shared with the Potterton Promax (Baxi Group cross-reference). Always confirm the full model number before ordering.
Call our helpline if you’re unsure which diverter valve or actuator your boiler requires: 0330 124 5678.
Installation Notes
Full diverter valve body replacement requires draining the heating circuit. Actuator motor replacement can typically be done without draining — power off, unclip the actuator, fit the new motor, restore power.
Gas Safe engineer should carry out the work and test both CH and DHW modes after fitting.
Need a Recommended Installer?
- HGB Heating Kent — Gas Safe engineers, Baxi specialists, Kent and Medway
- Boiler Sense — Certified boiler specialists, Kent and South East London