F17
Ideal
Triac / Solid-State Output Failure
F17 displayed and thermostat cannot drive zone valve or boiler despite correct wiring
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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
Failed solid-state switching device on thermostat PCB, Overload from multiple valves on one output, Short circuit event in past damaging output stage
How to Fix / Troubleshooting
Safety first: Isolate mains power before working on wiring.
Steps:
- 1. Check load rating: Confirm that the total load (zone valves, relays) on the thermostat output does not exceed the maximum current specified by Ideal.
- 2. Test output voltage: With power on and thermostat calling for heat, measure voltage at the CH/HW output terminal. If no voltage is present and F17 is shown, the output device is likely failed.
- 3. Bypass test (for professionals): At the wiring centre, briefly link permanent live to the CH/HW circuit to confirm the boiler and valves operate. Do not leave this link in place; it is for testing only.
- 4. Reduce load: If multiple valves are connected, consider using an intermediate relay board so the thermostat only drives a relay coil, not all valves directly.
- 5. Replace thermostat: A failed triac or solid‑state output is not user‑repairable; replace the thermostat head.
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Repair Difficulty
Hard
4/5
Required Part
Ideal Smart Thermostat Main PCB
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