F23
Protherm
Flow/Return Temperature Difference Too High
F23 displayed, furnace cycles rapidly, poor heating performance
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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
Blocked radiator circuits, Partially closed valves, Undersized or failing circulation pump, Air in system causing poor flow
How to Fix / Troubleshooting
Safety first: Turn off power and allow system to cool slightly before bleeding radiators.
- Step 1 – Open valves: Ensure all radiator and zone valves are open, especially near the furnace.
- Step 2 – Bleed air: Bleed radiators starting from the lowest to highest floors. Top up system pressure as needed.
- Step 3 – Check pump speed: Many Protherm pumps have adjustable speed. Set to a higher speed if the system is large.
- Step 4 – Technician flow check: A technician can measure temperature differential and verify pump performance, replacing the pump if necessary.
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Repair Difficulty
Medium
3/5
Required Part
Circulation Pump
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