H11
Worcester Bosch
Insufficient Flow / Flow Switch Fault
Boiler displays H11, often associated with flow sensor or pump issues.
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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
Stuck flow switch, Blocked system filter, Pump not running or airlocked, Closed isolation valves
How to Fix / Troubleshooting
Safety first: Turn off power before touching valves or filters.
- Check isolation valves: Ensure the flow and return isolation valves under the boiler are fully open (slot in line with the pipe).
- Check any external filter: If you have a system filter (e.g. Worcester Bosch Greenstar filter), follow the manufacturer's instructions to clean it.
- Bleed radiators and pump: Remove air from the system and pump (if bleed screw fitted), then top up pressure.
- Engineer tasks: An engineer should test the flow switch/sensor, verify pump operation, and clear any internal blockages.
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Repair Difficulty
Medium
3/5
Required Part
Flow Switch / Flow Sensor
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