How to Replace a Boiler Pump (UK, 2026)

Seized vs failed

A dead pump is silent. A seized pump hums but doesn't circulate. Free the impeller with the centre screwdriver slot before condemning — a 5-second spin often restores flow after summer standstill.

Modern boilers use PWM pumps

Old fixed-speed pumps are gone. Modern PWM pumps modulate 30–100 % on the boiler PCB's PWM signal. Fit only PWM-compatible replacements or the boiler will lock out on F75/E133.

• Worcester Greenstar 8000 — pump head 87172043380 (Wilo Yonos PARA).
• Vaillant ecoTEC plus — 0020221215 (Grundfos UPM3).
• Baxi 800 — 720018001.
• Ideal Logic — 175593 pump replacement kit.

Fit and bleed

Fit new pump gaskets (never reuse). Bleed via the pump vent screw with a 2 mm slot driver until water — not air — weeps.