Boiler displays E12, which may be accompanied by noisy operation or rapid cycling.

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

Blocked system or heat exchanger, Pump running at an incorrect speed, Air in the system, Incorrect bypass setting.

Safety first: Turn off the boiler and allow it to cool before bleeding radiators or opening any valves.

User checks:

Bleed radiators to remove trapped air and top up the pressure afterwards.
Ensure all radiator valves are open and that thermostatic radiator valves (TRVs) are not all closed.

Engineer checks:

Check the pump speed setting and verify adequate circulation through the system.
Inspect and clean any system filter or strainer.
Assess the primary heat exchanger and system pipework for sludge; powerflush the system if necessary.
Verify that an automatic bypass valve (if fitted) is correctly set.

Resolving circulation issues usually clears E12 faults.

Hard 4/5

Central Heating Pump

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