E08
Main
Pump Circulation Fault
Boiler intermittently shuts down with E08, especially when heating demand is high
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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
Seized or weak pump, Airlock in primary circuit, Blocked system filter, Sludge in Main primary heat exchanger
How to Fix / Troubleshooting
Safety: Isolate power before touching the pump or opening any bleed points. Water may be hot.
- Listen and feel for pump: On a call for heat, place a hand on the pump body (if accessible). A humming noise without vibration suggests a seized rotor.
- Bleed the pump: Some Main boilers have a bleed screw on the pump front. With power off and a cloth ready, carefully loosen the screw to release trapped air, then retighten.
- Check system filter: If a magnetic or inline filter is fitted on the return to the boiler, isolate it and clean out sludge following the manufacturer’s instructions.
- Engineer tasks:
- Check pump head for free rotation and replace the Main pump assembly if seized or noisy.
- Inspect the primary heat exchanger for blockage and flush the system if heavily sludged.
- Verify correct pump speed setting and flow rate for the connected system.
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Repair Difficulty
Medium
3/5
Required Part
Circulating Pump
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