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At the heart of every comfortable home is a water heater, diligently ensuring that hot water is available at a moment’s notice. But what exactly goes on inside this household workhorse? Let’s delve into the anatomy of a water heater, understanding its key components and the vital roles they play.

1. Tank

The most recognizable part of many water heaters, the tank is where water is stored and heated. It typically has a capacity ranging from 20 to 80 gallons. Inside, it’s lined with a protective material to prevent rusting, usually glass. Insulation surrounds this inner lining to keep the heated water warm.

2. Dip Tubes

There are two primary tubes in a water heater tank: the cold water dip tube and the hot water outlet. The former brings in cold water from your home’s supply to the bottom of the tank, while the latter allows hot water to exit from the top.

3. Heating Mechanism

  • Gas Burners: In gas water heaters, burners situated below the tank heat the water. They operate similarly to the burners on a gas stove but on a larger scale.

  • Electric Heating Elements: Electric water heaters utilize one or two heating elements, similar to those in an electric oven, to warm the water. These elements are typically located in the middle and near the bottom of the tank.

4. Thermostat

This component maintains the water at your desired temperature. Once the water temperature drops below the preset level, the thermostat triggers the heating mechanism to warm the water. In electric heaters, there’s often a separate thermostat for each heating element.

5. Pressure Relief Valve

Safety is paramount, and this valve plays a critical role in preventing potential hazards. If the pressure or temperature inside the tank exceeds safe levels, this valve releases the excess, ensuring the tank doesn’t explode.

6. Drain Valve

Situated near the base of the tank, the drain valve is essential for maintenance and repairs. It allows water to be emptied from the tank, facilitating tasks like flushing out sediment or replacing the heating elements.

7. Anode Rod

Arguably the unsung hero of prolonging a water heater’s life, the anode rod attracts corrosive elements. Made from magnesium or aluminium with a steel core, it sacrifices itself over time, corroding in place of the tank’s inner lining. Regular inspection and replacement of the anode rod can significantly increase the heater’s lifespan.

8. Expansion Tank

Some modern systems, especially in areas with ‘closed-loop’ plumbing systems, incorporate an expansion tank. As the water heats up, it expands. This tank provides space for that extra volume, preventing excessive pressure build-up in the primary tank.

9. T&P Valve (Temperature & Pressure Relief Valve)

The T&P valve is a safety feature ensuring that the water heater operates within safe temperature and pressure limits. If either parameter exceeds set thresholds, the T&P valve will open, releasing water and lowering the tank’s internal temperature and pressure.

10. Flue

Exclusive to gas water heaters, the flue is a vent that removes combustion gases produced by the burner. It runs through the centre of the tank and ensures the safe exhaust of these gases, typically through the roof.

11. Heat Traps

Heat traps, present in both inlet and outlet fittings, prevent convection currents, which can cause heat to escape from the tank. They can improve energy efficiency by ensuring heat remains in the tank.

12. Sacrificial Anode Rod

The anode rod is made of magnesium or aluminium and is designed to corrode over time. Its “sacrificial” nature means that it will deteriorate before the steel tank does, thus prolonging the life of the water heater. It’s crucial to check this rod periodically and replace it when necessary.


The water heater, often overlooked unless malfunctioning is a marvel of engineering and design. Each component, from the humble drain valve to the critical pressure relief mechanisms, works in tandem to provide a steady supply of hot water. Understanding its anatomy not only satiates curiosity but also equips homeowners with the knowledge that can aid in maintenance, troubleshooting, and informed decision-making when investing in a new unit. The next time you enjoy a warm shower or wash your hands in the sink, you’ll have a newfound appreciation for the intricate dance of components that makes it all possible.