Can I clean the old one?

Rinse and refit if the trap body is undamaged, but always fit new seals.

22 mm external pipe rule?

Yes — post-2018 the run outside the wall must be 32 mm insulated per BS 6798.

Only if the Ariston Clas ONE 30 is in warranty — Ariston require log of any part swap for labour claims.

Renew the internal condensate trap on Ariston Clas ONE 30 when you get D5, F1 or E133 pressure-switch faults after a service.

The trap on Ariston Clas ONE 30 snaps into the case bottom — flood with clean water before refitting to prime the U-bend.

Check the external condensate pipe fall (2.5° minimum) at the same time to avoid a repeat freeze-up.

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.

Can I clean the old one?: Rinse and refit if the trap body is undamaged, but always fit new seals.
22 mm external pipe rule?: Yes — post-2018 the run outside the wall must be 32 mm insulated per BS 6798.
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.

Shop the spares

Browse boiler spares — 14,820 live parts.