Viessmann
Insufficient DHW Heating
Water heater produces lukewarm water only, cannot reach set temperature
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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
Scaled plate heat exchanger reducing heat transfer, Gas valve not reaching full modulation, Incorrect gas pressure, Partially blocked burner or injector
How to Fix / Troubleshooting
Safety: Turn off power and gas before working on gas or hydraulic components.
- Check DHW setpoint: Confirm the DHW temperature is set high enough on the control panel.
- Reduce flow rate: Temporarily reduce the hot water flow at the tap. If temperature increases, the heater may be undersized or restricted by scale.
- Descale plate heat exchanger: Isolate and chemically descale the DHW plate heat exchanger to restore heat transfer.
- Inspect burner: Clean burner ports and check for even flame distribution. Have gas pressures and valve modulation checked by a licensed technician.
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Repair Difficulty
Hard
4/5
Required Part
Plate Heat Exchanger
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