F11 error, furnace runs but central heating does not get hot, or temperature control is erratic

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Faulty pump speed feedback (on modulating pumps), Incorrect wiring to Glow-worm pump connector, Blocked pump or seized rotor, Flow sensor malfunction (on models with flow sensor)

How to Fix / Troubleshooting

Safety: Isolate power and allow system to cool. Water may be hot under pressure.

Technician checks:

Verify that the circulation pump runs when there is a heat demand; listen and feel for vibration.
Remove the pump head and check the rotor for blockage or seizure; free or replace as necessary.
Check any flow sensor or pump feedback wiring to the PCB.
Bleed air from the pump and system using bleed screws and radiator vents.
Replace the pump or flow sensor if defective.

Repair Difficulty

Hard 4/5

Required Part

Circulation Pump

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