Protherm
Expansion Vessel Failure / Over‑Pressurization
System pressure rises excessively when heating and relief valve discharges water
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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
Flat or ruptured expansion vessel on Protherm unit, Incorrect pre‑charge pressure, Overfilled system, Faulty pressure relief valve seating
How to Fix / Troubleshooting
Safety first: Allow system to cool. Hot water discharge can cause burns.
- Step 1 – Check cold pressure: When cold, set system pressure to about 1.2–1.5 bar.
- Step 2 – Observe pressure rise: If pressure climbs above 3 bar when heating, the expansion vessel is likely not functioning.
- Step 3 – Vessel pre‑charge (technician): A technician can isolate and check the vessel air charge, re‑pressurizing or replacing it if the diaphragm is damaged.
- Step 4 – Relief valve: If the relief valve drips continuously after a high‑pressure event, it may need replacement.
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Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel
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