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Sight glass
A clear (usually borosilicate) tube on the side of a steam boiler that shows the current water level at a glance — common on traditional commercial machines.
Category: Water System
A vertical glass tube on the side of a steam boiler that shows the water level inside. Used as a visual reference to confirm the boiler is correctly filled.
Why it matters — A sight glass lets you confirm the boiler level at a glance — essential for diagnosing autofill issues, confirming boiler health, and checking after a cleaning cycle.
Good to know
- Sight glasses can crack from thermal shock — replace immediately if cracked, as a failed sight glass can drain the boiler at speed.
- Scale builds up on the inside of sight glasses over time. Periodic descaling restores visibility.