How to Replace the Diverter Valve on a Vaillant ecoTEC Plus 418 (UK)
Step-by-step UK guide to replacing the 3-way diverter valve on a Vaillant ecoTEC Plus 418. Part numbers, torques, commissioning.
The part
Replace the diverter valve on Vaillant ecoTEC Plus 418 when hot water runs cold on demand or the boiler cycles between CH and DHW.
Isolate safely
Drain to below the diverter body via the CH drain-off. On Vaillant ecoTEC Plus 418 the diverter is a cartridge design — pull the retaining clip and lift out.
Fit and commission
Fit new O-rings, silicone-grease the cartridge and align the actuator drive slot before refitting the motor.
Recommission checklist
Refill the Vaillant ecoTEC Plus 418 to 1.2 bar cold. Bleed high-point radiators and the internal AAV.
Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.
Frequently asked questions
- Actuator or cartridge only?
- Diagnose first: manually push the actuator pin. If it moves freely, replace the actuator only; if the pin sticks, the cartridge is scaled.
- Any special tools?
- A brass spanner or the OEM diverter tool avoids cracking the plastic body on Vaillant ecoTEC Plus 418.
- Do I need to notify the manufacturer?
- Only if the Vaillant ecoTEC Plus 418 is in warranty — Vaillant require log of any part swap for labour claims.
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