How to Replace a Boiler Siphon Trap (UK)
Same as condensate trap but branded 'siphon' by Baxi, Ideal, Vaillant. Part numbers and fit sequence.
BaxiIdealVaillantWorcester Bosch
Siphon vs P-trap
Modern siphon traps flush intermittently (100 ml every 2 min under load). Older P-traps trickle continuously. Blockage patterns differ — siphons block at the neck, P-traps at the outlet.
OEM part numbers
- Baxi 800 — 720072201.
- Ideal Logic — 173950.
- Vaillant ecoTEC — 0020155086 (with silicone connector).
- Worcester Greenstar 8000 — 87161029130.
Fit
Remove old trap complete, flush with warm water + 5 % vinegar to descale the outlet spigot. Refit with new O-ring.
Frequently asked questions
- Should I clean or replace the siphon?
- Clean if <3 years old and shell is unstained. Replace if plastic is discoloured or brittle.
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