E18
ACV
Flow Rate Too Low / Flow Sensor Differential Fault
Display shows E18, unit may overheat or cycle rapidly
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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
Blocked ACV plate heat exchanger, Closed or partially closed isolation valves, Air in primary circuit, Undersized or failing circulation pump
How to Fix / Troubleshooting
Safety: Allow the system to cool before opening any components. Isolate power and close valves as needed.
- 1. Check valves: Ensure all isolation valves around the heater and primary circuit are fully open.
- 2. Bleed air: Use automatic and manual air vents to remove air from the primary circuit. Re-pressurize as needed.
- 3. Inspect strainers: Clean any Y-strainers or filters on the primary side that may be restricting flow.
- 4. Plate heat exchanger: On ACV units with a separate plate heat exchanger, check for temperature difference across the exchanger. A large difference with low flow suggests blockage. Descale or replace the plate heat exchanger.
- 5. Pump performance: Verify that the pump is correctly sized and operating at the required speed setting.
If E18 persists, a technician should measure actual flow and temperature differential to diagnose further.
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Repair Difficulty
Hard
4/5
Required Part
Plate Heat Exchanger
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