E04
Laars
Low Water Pressure / Flow Error
Boiler displays E04; often indicates low water pressure or flow on some Laars controls.
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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
Low system pressure, Air lock, Blocked strainer or filter, Faulty flow switch or sensor
How to Fix / Troubleshooting
Safety first: Let the system cool before opening any valves or strainers.
- Check pressure gauge: Ensure system pressure is within the recommended range. Add water if trained to do so.
- Bleed air: Remove air from radiators and vents.
- Clean strainers: If your Laars boiler has a system strainer, isolate and clean it to restore flow.
- Inspect flow switch: Verify wiring and that the paddle or turbine is not stuck (requires disassembly by a technician).
When to call a professional: If E04 persists, a technician should check the flow sensor and system hydraulics.
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Repair Difficulty
Medium
3/5
Required Part
Flow Switch / Flow Sensor
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