F.76
Vaillant
Primary Heat Exchanger Thermal Fuse Triggered
F.76 primary heat exchanger overheat; appliance locked out
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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
Severe overheating of primary heat exchanger, Blocked or failed pump, Blocked heat exchanger, Faulty or bypassed safety devices
How to Fix / Troubleshooting
Safety: This indicates a serious overheat event. Isolate power and gas immediately. Do not attempt to reset repeatedly without finding the cause.
- Inspect circulation: Check pump operation, system pressure, and all valves. Restore proper circulation.
- Check for blockages: Inspect the primary heat exchanger for scale or sludge. Descale or replace if necessary.
- Replace thermal fuse: The thermal fuse on the heat exchanger is a one-shot safety device and must be replaced with the correct Vaillant part.
- Full safety check: A qualified Vaillant engineer should perform a full safety and combustion check before returning the appliance to service.
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Repair Difficulty
Professional Required
5/5
Required Part
Primary Heat Exchanger Thermal Fuse
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