Potterton
Over-Pressurisation / Expansion Vessel Failure
Boiler pressure rises rapidly when heating is on and discharges water outside
Advertisements
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.
Advertisements
Possible Causes
Flat or ruptured expansion vessel, Blocked expansion vessel connection, Incorrect system fill pressure, Faulty pressure relief valve
How to Fix / Troubleshooting
Safety first: Allow the system to cool before checking pressure. Water from the discharge pipe may be hot.
User checks:
- Note the cold pressure and the hot pressure when heating is on; report this to the engineer.
Engineer checks:
- Isolate and drain pressure from the system, then check the expansion vessel air charge with a tyre gauge.
- Recharge the vessel to the manufacturer-specified pressure (typically around 0.8–1.0 bar) or replace if the diaphragm has failed.
- Ensure the vessel connection pipe is not blocked.
- Replace the pressure relief valve if it has been repeatedly lifting.
Correct expansion vessel operation is essential to prevent pressure-related faults.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements