How to Replace the Diverter Valve on a Ariston Clas ONE 30 (UK)
Step-by-step UK guide to replacing the 3-way diverter valve on a Ariston Clas ONE 30. Part numbers, torques, commissioning.
The part
Replace the diverter valve on Ariston Clas ONE 30 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 Ariston Clas ONE 30 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 Ariston Clas ONE 30 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 Ariston Clas ONE 30.
- Do I need to notify the manufacturer?
- Only if the Ariston Clas ONE 30 is in warranty — Ariston require log of any part swap for labour claims.
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