Boiler shows A23, communication error with remote controller or cascade manager

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

Broken BUS cable, reversed polarity on Herz BUS terminals, incompatible controller firmware, electrical interference on BUS line

Safety: Isolate power before changing BUS wiring.

Check wiring: Verify that the BUS wires are connected to the correct terminals and polarity (+/−) on both boiler and Herz controller.
Inspect cable: Look for damage, joints, or splices that may cause intermittent contact.
Reduce interference: Keep BUS cables away from mains power cables and sources of electrical noise.
Reset devices: Power cycle both the boiler and controller. If A23 persists, consult Herz documentation for firmware compatibility and update if required.

Medium 3/5

Herz BUS communication module

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