Service Boiler Expansion Tank Air Charge
Why it matters
A waterlogged expansion tank (no air precharge) causes the relief valve to weep continuously, pressurizing the system. This shortens boiler life and causes leaks.
Stop forgetting to do this.
Hearth generates a personalized maintenance schedule so you never miss another service boiler expansion tank air charge.
How to do it
- 1
Locate the expansion tank (typically a hanging tank near the boiler); tap it with a hammer—a hollow sound = good, a full/heavy sound = waterlogged.
- 2
If waterlogged, turn off the boiler and allow to cool.
- 3
Close the isolation valve below the tank (if present) or the main water supply.
- 4
Open the drain valve at the bottom of the tank; let water drain into a bucket.
- 5
Once empty, use a tire-pressure gauge and pump to check the air precharge (typically 12–20 psi; check boiler manual).
- 6
If precharge is low, add air with a bicycle pump; if tank won't hold air, call a plumber to replace the tank bladder.