Oso
Failed Expansion Vessel Diaphragm
Oso water heater’s expansion vessel frequently discharges water or loses charge.
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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
Ruptured diaphragm, Incorrect pre‑charge pressure, Undersized vessel for system volume, High incoming mains pressure
How to Fix / Troubleshooting
Safety first: Isolate the water heater and relieve system pressure before checking the expansion vessel.
- Check pre‑charge: With no water pressure on the vessel, measure air charge at the Schrader valve. Recharge to the value specified by Oso.
- Test for water at valve: If water comes out of the Schrader valve, the diaphragm has failed and the vessel must be replaced.
- Replace vessel: Isolate, drain as needed, and install a new Oso‑compatible expansion vessel of correct size.
- Verify pressure control: Ensure the inlet pressure reducing valve is functioning correctly to prevent over‑pressurization.
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Repair Difficulty
Hard
4/5
Required Part
Oso expansion vessel
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