Boiler shows A18, heating flow temperature rises too quickly then burner shuts down

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

Failed or air-locked circulation pump, Pump set to too low speed, Blocked system filter, Closed isolation valves on flow/return

Safety: Allow boiler to cool and isolate power before touching the pump.

Steps:

Ensure the flow and return isolation valves under the boiler are fully open.
Bleed air from the pump vent screw (if fitted) until water flows steadily.
Check and clean any inline filter on the return pipe.
Increase the pump speed setting on the IVT boiler if adjustable.
If the pump does not run or is noisy, a technician should replace the pump cartridge or complete pump.

Medium 3/5

Primary Circulation Pump

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