Boiler shows A28, cascade system not responding correctly

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 cascade wiring between Herz boilers, duplicate master configuration, BUS address conflict, faulty cascade module

Safety: Isolate power to all boilers in the cascade before altering wiring.

Check roles: Verify that only one Herz boiler is configured as master and others as slaves according to the cascade scheme.
Inspect BUS wiring: Ensure the cascade BUS is daisy-chained correctly with proper polarity and termination if required.
Set addresses: Assign unique addresses to each boiler in the installer menu.
Test individually: Run each boiler in standalone mode to confirm correct operation before re-enabling cascade.

Hard 4/5

Herz cascade control module

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