Viessmann
Short Cycling on DHW Demand
Water heater repeatedly turns on and off rapidly when hot water is used
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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
Oversized appliance for low flow demand, Flow sensor misreading, Scale in heat exchanger causing rapid temperature rise, Minimum burner output too high for system
How to Fix / Troubleshooting
Safety: Do not alter gas settings yourself. Work on water-side components only unless qualified.
- Increase flow: Open the hot tap further or use a larger outlet to see if cycling reduces. Very low flows may be below the stable modulation range.
- Clean flow sensor and filters: Ensure accurate flow detection by cleaning the DHW flow sensor and inlet filter.
- Descale heat exchanger: Remove limescale from the plate heat exchanger to slow the temperature rise and reduce cycling.
- Professional adjustment: A technician can adjust parameters or burner settings within Viessmann guidelines to minimize short cycling.
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Repair Difficulty
Medium
3/5
Required Part
DHW Flow Sensor
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