How to Replace a Boiler Diverter Valve (UK, 2026)
Swap a Worcester, Vaillant, Baxi or Ideal diverter valve. OEM cartridge numbers, symptoms and refit torque.
Worcester BoschVaillantBaxiIdealGlow-worm
Symptoms of a stuck diverter
Hot water works but central heating is cold — or vice versa. The valve motor is stuck part-open, blending flow into the wrong circuit. A 5-second manual push on the diverter stem confirms free movement.
- No CH but hot water fine — diverter stuck on DHW side.
- Lukewarm rads and boiling taps — diverter partially seized.
- Both circuits weak — check pump before condemning the diverter.
OEM cartridges by brand
- Worcester Greenstar 24i/28i/30i — cartridge 87186445880.
- Vaillant ecoTEC plus — full assembly 0020132682, motor head 178984.
- Baxi 800/EcoBlue — cartridge 720030401.
- Ideal Logic/Vogue — 173537 diverter cartridge.
- Glow-worm Ultimate3 — 0020132683 (Vaillant Group shared).
Refit without cross-leaks
Grease the new O-rings with silicone (never petroleum). Hand-tighten the retaining clip, then confirm the flow switch clicks over on a hot tap open. Bleed the boiler through the auto air vent — trapped air throws an F22 within 24 h.
Frequently asked questions
- How long does a diverter valve last?
- Typically 7–10 years on a UK combi. Hard-water areas (>300 mg/L) can see failure at 4–5 years — fit a scale reducer to extend life.
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