Junkers
Boiler not responding to room thermostat
Boiler runs continuously and overheats rooms even when thermostat is turned down
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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
Stuck relay on PCB, Faulty room thermostat, Shorted thermostat wiring, Incorrect controller configuration
How to Fix / Troubleshooting
Safety: Overheating is uncomfortable but not usually an immediate hazard; however, it wastes energy.
- Check thermostat: Ensure the room thermostat is set correctly and not located near a heat source.
- Test response: Turn the thermostat fully down; the boiler should stop calling for heat. If it continues, suspect wiring or PCB.
- Inspect wiring: Check thermostat cable for shorts or bridging at the boiler terminals.
- Technician tasks:
- Test thermostat operation and replace if faulty.
- Check PCB output relays and replace the main PCB if a relay is stuck closed.
- Verify correct configuration of Junkers controller (e.g., weather compensation vs. room control).
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Repair Difficulty
Medium
3/5
Required Part
Room Thermostat
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