Water Heater Glass Lining — What It Is and How It Protects Your Tank
Published: July 21, 2026 — CANRO Heating & Cooling — Greater Vancouver, BC
What Glass Lining Does
All modern tank water heaters have a glass (vitreous enamel) lining bonded to the interior steel tank at 850°C. The glass lining is the primary corrosion barrier — it prevents water from contacting the steel tank. The sacrificial anode rod is the secondary protection that protects any small areas where the glass lining may have imperfections.
Why Glass Lining Fails
Over time, the glass lining can develop micro-cracks from: thermal cycling (heating and cooling stresses), physical impact during installation or maintenance, or manufacturing defects. Once water reaches the steel through a crack, corrosion begins rapidly unless the anode rod is active.
Lifespan and Replacement
The glass lining typically lasts 8-12 years — matching the standard water heater warranty. Once the lining fails and corrosion starts, the tank cannot be repaired — replacement is the only option. Maintaining the anode rod extends the effective lifespan of the glass lining by preventing corrosion at crack points.