Boiler fires but quickly overheats, flow pipe gets very hot while return stays cool, some radiators cold.

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

Seized pump rotor, Electrical failure of pump motor, Blocked pump impeller due to sludge, Incorrect pump speed setting

Safety: Isolate power and allow system to cool before touching the pump or pipework.

User checks:

Place a hand on the pump body (if accessible) to feel for vibration or noise indicating operation (do not touch if hot).

Engineer steps:

Confirm voltage at the pump terminals when there is a call for heat.
Remove the pump head and check the impeller for blockage; free or replace as necessary.
Set the pump speed according to system design and Grant recommendations.
Replace the circulating pump if electrically failed or excessively noisy.

Medium 3/5

Circulating pump

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