What is likely happening
An expansion tank absorbs the change in water volume as the system heats. When it waterlogs or loses its air charge, pressure spikes and the relief valve may discharge.
What you can safely check
- Tap the tank: a waterlogged tank sounds solid all the way up.
- Watch whether pressure jumps sharply when the boiler heats up.
What an inspector will look at
- Tank air charge and bladder
- Relief valve
- Fill valve setting
Does this affect compliance?
The tank itself is rarely an inspection item, but the pressure problems it causes are.
When it becomes urgent
Urgent if the relief valve is discharging.
We can help with this
Boiler inspection is something Insparisk does nationwide. To see the local rules for your building, open this in the interactive Problem Solver.
Request boiler inspectionTalk to an advisorGeneral guidance only, not a substitute for a licensed inspection or emergency services. For any gas odor, carbon monoxide alarm, fire, or trapped occupant, call 911 first.