Water heater’s hot water is discoloured (brown or black) when first run
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.
Possible Causes
How to Fix / Troubleshooting
Safety first: Discoloured water is usually not immediately dangerous but may indicate corrosion. If water has an oily film or chemical smell, do not use it.
User checks:
- Run the hot tap for several minutes to see if the discolouration clears.
- Check if the same discolouration occurs on the cold supply; if so, the issue may be with the mains or pipework, not the heater.
Engineer steps:
- Inspect the DHW plate heat exchanger and internal DHW pipework for corrosion.
- Flush the DHW circuit and, if necessary, replace affected components.
If discolouration persists or worsens, consult both a plumber and the water supplier.
Repair Difficulty
Required Part
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