F22
Protherm
Low Water Content / Dry-Fire Protection
F22 displayed, appliance does not start, may indicate dry operation or low water content
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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
Insufficient system pressure (on sealed systems), Air in primary circuit, Blocked automatic air vent, Faulty pressure sensor (if fitted)
How to Fix / Troubleshooting
Safety first: Turn off power. If the unit is connected to a sealed system or cylinder, allow it to cool before topping up pressure.
- Check system pressure: On models with a pressure gauge, ensure pressure is within Protherm's recommended range. Top up via filling loop if necessary.
- Bleed air: Open manual air vents and ensure automatic air vents are not capped off.
- Inspect pressure sensor: If pressure is correct but F22 persists, test and replace the water pressure sensor if present.
- Check for leaks: Inspect the system for visible leaks that may be causing pressure loss.
Warning: Never operate the heater without water; this can destroy the heat exchanger and is unsafe.
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Repair Difficulty
Medium
3/5
Required Part
Water Pressure Sensor
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