F.24
Vaillant
Rapid Temperature Rise / Low Water Content
F.24 displayed; rapid temperature rise detected, unit shuts down quickly
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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
Severely restricted flow through heat exchanger, Pump not running (if present), Airlock in heat exchanger, Incorrectly set or closed bypass, Blocked internal waterways
How to Fix / Troubleshooting
Safety: Turn off power and gas. Allow the unit to cool fully.
- Verify water flow: Open a hot tap fully and check that flow is strong and stable. Weak flow can cause rapid temperature rise.
- Check for blockages: Inspect inlet filters, flow restrictors, and the plate/primary heat exchanger for scale or debris. Clean or replace as needed.
- Bleed air: Use bleed points to remove air from the heat exchanger and pump. Air pockets can cause local boiling.
- Check pump (if applicable): Ensure the circulation pump is powered and spinning freely. Replace if seized or intermittent.
- Reset and monitor: After correcting flow issues, reset the appliance and run it while monitoring temperatures. If F.24 recurs, further hydraulic checks by a Vaillant engineer are recommended.
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Repair Difficulty
Hard
4/5
Required Part
Circulation Pump
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