20
Vokera
External Control / Room Thermostat Circuit Fault
Boiler displays 20, no response to thermostat, heating will not start
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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
Open circuit room thermostat wiring, Faulty external programmer, Incorrect wiring at boiler terminal block, PCB input fault
How to Fix / Troubleshooting
Safety first: Isolate electrical power before accessing wiring terminals.
- Check controls: Ensure the room thermostat and programmer are calling for heat (set to maximum temperature and constant on).
- Check boiler mode: Confirm the boiler is not in summer/DHW-only mode if heating is required.
- Engineer checks:
- Test for continuity across the room thermostat contacts when calling for heat.
- Inspect wiring at the boiler control terminals for loose or broken conductors.
- Temporarily link the room stat terminals at the boiler (for test only) to see if the boiler responds.
Any permanent wiring changes must comply with Vokera wiring diagrams and local regulations.
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Repair Difficulty
Medium
3/5
Required Part
Room Thermostat / Control Wiring
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