De Dietrich Heating Circuit Demand / Diverter Fault

Boiler produces hot water but no central heating

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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.

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Possible Causes

Room thermostat not calling for heat, faulty diverter valve stuck in DHW position, faulty heating zone valve, wiring fault

How to Fix / Troubleshooting

Safety: Isolate power before working on controls or valves.

  • Check controls: Ensure the room thermostat or De Dietrich controller is set to a higher temperature than room temperature and that any programmer is calling for heat.
  • Check diverter valve: If DHW works but radiators stay cold, the diverter valve may be stuck. Listen for movement when switching between DHW and CH.
  • Zone valves: On systems with external motorised valves, check that the heating valve opens and its end-switch operates.
  • Technician tasks: Test control circuits, replace faulty thermostats, zone valves, or diverter valve actuators.
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Repair Difficulty

Medium 3/5

Required Part

3-Way Diverter Valve
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