Bosch
No Central Heating Demand / Control Circuit Fault
Boiler has power (display on) but does not fire for central heating; radiators stay cold.
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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 or programmer not calling for heat, Faulty external controls wiring, Stuck diverter valve in DHW position (combi), PCB not responding to CH demand
How to Fix / Troubleshooting
Safety: Isolate power before opening any wiring centers.
Steps:
- Check that the room thermostat is set above room temperature and that the programmer is in an ON or HEAT mode.
- On the boiler, ensure CH is enabled and not in summer/DHW‑only mode.
- If you have a combi boiler, run a hot tap; if hot water works but CH does not, the diverter valve may be stuck in DHW position.
- Inspect the wiring center (if present) for loose connections to the boiler's call‑for‑heat terminals.
Control wiring faults and diverter valve replacement should be handled by a heating engineer.
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Repair Difficulty
Medium
3/5
Required Part
Diverter Valve Assembly
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