Boiler displays E18, often associated with low system water content or flow rate

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.

Possible Causes

Blocked system filter, Closed isolation valves, Airlock in system, Faulty flow switch or sensor

Safety first: Allow the system to cool before opening any bleed points.

Check valves: Ensure all flow and return isolation valves under the boiler and any zone valves are open.
Bleed radiators and high points: Remove trapped air from radiators and any automatic air vents. Top up pressure as needed.
Clean system filter: If fitted, isolate and clean the magnetic/mesh filter on the return line.
Engineer flow sensor check: On models with an internal flow switch or sensor, the engineer should inspect, clean, or replace the device if it is sticking.

Medium 3/5

Primary Flow Switch / Flow Sensor

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