A05
Hoval
Incorrect Combustion / Ignition Control Fault
Boiler shows A05, attempts to start but shuts down quickly, sometimes with loud ignition noise
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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
Incorrect gas/air ratio, Blocked or contaminated burner, Faulty gas valve modulation control, Defective combustion control PCB
How to Fix / Troubleshooting
Warning: Combustion adjustments must only be made by a certified Hoval technician with a calibrated flue gas analyser.
- Visual inspection: Check burner and combustion chamber for soot or signs of incomplete combustion. Heavy sooting indicates incorrect gas/air ratio or blocked burner.
- Check flue integrity: Ensure all flue joints are sealed and correctly assembled according to Hoval installation instructions. Air leaks can disturb combustion.
- Reset and observe: Reset the boiler and observe ignition from a safe distance. If there are repeated loud bangs or delayed ignition, switch off the boiler and do not use it.
- A Hoval technician should then:
- Check burner condition and clean/replace if necessary.
- Verify gas valve modulation and inlet pressure.
- Perform combustion analysis and adjust settings within Hoval specifications.
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Repair Difficulty
Professional Required
5/5
Required Part
Gas Valve Assembly
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