Boiler Expansion Vessel Problems
A waterlogged expansion vessel causes pressure swings and PRV discharge — recharging or replacing fixes it.
The expansion vessel absorbs the pressure increase as water heats. When it fails, you get pressure fluctuations and relief-valve discharge.
Signs of failure
Pressure that climbs high when hot and drops when cold, water discharging from the pressure-relief valve, and frequent re-pressurizing all point to a waterlogged or failed expansion vessel.
The fix
A technician can sometimes recharge the vessel with the correct air pre-charge; if the internal diaphragm has failed, the vessel is replaced or an external one fitted.
Key takeaways
- Big hot/cold pressure swings suggest the vessel
- PRV discharge often traces back to the vessel
- Recharging may restore it; failed diaphragms need replacement
- Don't just keep topping up pressure
Need help with your boiler?
Licensed, gas-certified technicians serving Greater Vancouver since 1999. CombiBoiler.ca — A division of ROMA Heating Ltd..