F37
Saunier Duval
Low System Pressure / Pressure Drop
Boiler shows F37 and stops, pressure fluctuates or drops
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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, Faulty pressure sensor, Safety valve passing water
How to Fix / Troubleshooting
Safety first: Allow the system to cool before checking for leaks or touching pipework.
Steps to check:
- Repressurise the system to 1.2–1.5 bar using the filling loop.
- Observe the pressure gauge over several hours of operation. If it drops, inspect for visible leaks on radiators, valves, and boiler connections.
- Check the safety valve discharge pipe outside for dripping water.
- If pressure rises above 3 bar when hot and then drops, the expansion vessel may be flat and needs recharging or replacement (engineer task).
Warning: Do not repeatedly top up without finding the cause of pressure loss; this introduces fresh oxygen and accelerates corrosion.
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Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel / Safety Valve
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