F37
Protherm
Low System Pressure / Frequent Pressure Loss
Boiler displays F37, pressure gauge fluctuates or drops frequently
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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
Leak in heating system, Faulty expansion vessel (loss of air charge), Faulty pressure relief valve passing water, Defective pressure sensor
How to Fix / Troubleshooting
Safety: Allow the system to cool before working on pressurized components.
Steps:
- Top up system pressure to the recommended level and monitor over several hours. If pressure drops, inspect for visible leaks at radiators, valves, and under the boiler.
- Check the discharge pipe from the pressure relief valve for signs of water discharge. If constantly wet, the PRV may be passing and should be replaced.
- Test the expansion vessel by checking the air charge with a pressure gauge (system side depressurized). Recharge to the manufacturer’s specified pressure or replace the vessel if the diaphragm has failed.
- Replace the water pressure sensor if it gives unstable readings despite stable actual pressure.
After repair: Re‑pressurize, bleed air, and confirm stable pressure without F37.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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