E25
Baxi
Primary Circuit Overheat / Flow Restriction
Boiler intermittently locks out with E25, often during heating demand, may be accompanied by noisy operation
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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
Sludge or scale in Baxi primary heat exchanger, Pump running at too low speed or partially blocked, Closed radiator valves causing poor flow, Air trapped in boiler or radiators
How to Fix / Troubleshooting
Safety first: Overheating can cause very hot surfaces. Allow the boiler to cool before bleeding or touching pipework.
User checks:
- Ensure most radiator valves are open to allow good circulation.
- Bleed radiators and any manual air vents near the boiler.
- Check system pressure and top up to 1.2–1.5 bar when cold.
- Reset the boiler and monitor whether radiators heat evenly without rapid cycling.
If E25 persists:
- A heating engineer should check pump performance, clean the primary heat exchanger, and consider a chemical flush or powerflush if the system is heavily sludged.
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Repair Difficulty
Medium
3/5
Required Part
Primary Heat Exchanger
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