Boiler shows H13, often linked to sensor calibration or temperature differential issues.

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

Incorrect readings from flow and return sensors, Sludge or blockage causing high temperature differential, Pump speed too low, Faulty NTC sensors

Safety first: Isolate power and allow the system to cool before bleeding or flushing.

Bleed system: Remove air from radiators and high points, then top up pressure.
Check all valves: Ensure all radiator and bypass valves are correctly set to allow adequate flow.
Engineer tasks: A professional should compare flow/return temperatures, test NTC sensors, adjust pump speed, and flush the system if sludge is present.

Hard 4/5

Flow and Return Temperature Sensors

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