Herz Unwanted Heating / Valve Bypass

Radiators get hot even when there is no call for heating

Advertisements

Safety Warning

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.

Advertisements

Possible Causes

Stuck diverter valve in Herz combi boiler, incorrectly wired external controls, internal leak through plate heat exchanger, faulty room thermostat

How to Fix / Troubleshooting

Safety: Pipes and radiators may be hot; take care when touching.

  • Check controller: Confirm that the Herz room thermostat or programmer is not calling for heat.
  • Test diverter valve: On combi models, run DHW only and feel if heating flow pipe warms significantly; if so, the diverter valve may be passing.
  • Inspect wiring: Ensure that external controls are wired according to the Herz wiring diagram and not permanently bridging the demand terminals.
  • Replace diverter valve: If internal bypass is confirmed, replace the Herz diverter valve cartridge or assembly.
Advertisements

Repair Difficulty

Medium 3/5

Required Part

Herz diverter valve
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements