E18
Sime
Heat Exchanger Flow Restriction
E18 error; Sime water heater may show low flow or blocked heat exchanger indication.
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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
Severe limescale in primary heat exchanger, Blocked internal waterways, Partially closed isolation valves, Blocked inlet filter
How to Fix / Troubleshooting
Safety: Turn off power, gas, and water. Allow the unit to cool fully.
Steps:
- Check valves and filters: Confirm inlet/outlet valves are fully open and clean the inlet filter.
- Assess water hardness: If you have hard water and the heater is several years old, scale is likely. You may notice reduced flow and hotter-than-normal outlet temperatures.
- Basic flush: Disconnect the heater from the water system and flush the heat exchanger with clean water in both directions to remove loose debris.
Professional help: Chemical descaling of the Sime primary heat exchanger should be done by a professional using appropriate pumps and descalers.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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