Boiler Expansion Vessel
The expansion vessel helps your heating system handle pressure changes as water heats up and cools down. When it fails, pressure problems and shutdowns often follow.
What the expansion vessel does
As water heats up, it expands. The vessel absorbs that extra pressure so the sealed system can keep operating within a safe range.
Signs the vessel may have failed
A failed vessel often shows up as unstable pressure, repeated lockouts or a relief valve discharging water when the system heats up.
Repair versus replacement
Some issues can be confirmed and corrected during diagnosis, but a failed vessel often needs replacement rather than repeated repressurising.
Frequently asked questions
Open a topic to read the full details.
Can this part always be repaired instead of replaced?
Not always. Some parts can be adjusted or re-pressurised, but many failed components need replacing once they are confirmed faulty.
Will replacing one part solve the whole issue?
Often it will, but the right answer depends on proper diagnosis. Symptoms like low pressure or no hot water can be caused by more than one component.
Should I book an engineer if the boiler still works sometimes?
Yes. Intermittent faults usually point to a part that is deteriorating and can lead to a full breakdown if ignored.
Book a boiler repair call-out
If the failed part is affecting heating, hot water or boiler pressure, we can diagnose the fault and advise on repair versus replacement.