Boiler shows A24, burner stops, system temperature rises unexpectedly

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 Herz circulation pump, blocked pump impeller, air lock in pump, failed pump relay on PCB

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

Listen for pump: When calling for heat, listen for the pump running. If silent, check the electrical connector at the pump.
Free impeller: On pumps with a front screw, remove it and gently turn the shaft with a screwdriver to free a stuck impeller.
Bleed pump: Loosen the vent screw slightly to release trapped air, then retighten.
Replace pump: If the pump does not run despite power being present, replace the Herz circulation pump assembly.

Hard 4/5

Herz circulation pump

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