Boiler shows E05, communication symbol flashing between boiler and Hoval TopTronic or room controller

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, Incorrect polarity on bus terminals, Too many devices on bus without proper termination, Faulty controller module

Safety: Isolate power before working on low-voltage wiring.

Check bus wiring: Verify that the two-wire bus from the Hoval boiler to the room controller or TopTronic module is continuous, correctly polarised, and not shorted.
Reduce devices: If multiple modules are connected, temporarily disconnect extras to see if communication is restored.
Terminations: Ensure any required bus termination resistors are installed as per Hoval documentation.
If E05 persists, a technician should test each module and replace the faulty one.

Medium 3/5

Control Bus Cable / Room Controller Module

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