Hot water running out faster than it used to? Here is why

1. Sediment in the bottom of the tank

This is the most common cause by a long way. Over the years, minerals in your water (mostly calcium and magnesium) settle to the bottom of the tank. In a Hunter region tank that has not been flushed in ten years, expect 3 to 6 kilograms of sediment.

That sediment takes up volume that used to be water. A 250L tank with 25L of sediment is functionally a 225L tank. It also insulates the heating element from the water, so the element runs hotter, fails earlier, and reheats slower.

Tell-tale signs: running out faster than you used to, rumbling or popping sounds during reheat, water sometimes looks slightly cloudy.

Fix: a tank flush. About $220 to $320 depending on tank condition. Can extend your tank life by 3 to 5 years.

2. Element decline (electric tanks)

Electric storage tanks have one or two heating elements. They wear out, especially when caked in sediment. A partially-failed lower element will still heat water but slowly, so you get warm water that runs out faster than it used to.

Tell-tale signs: water is warm rather than hot, takes much longer to reheat, sometimes you get a "trip" on the circuit.

Fix: element replacement. About $320 to $480 for one element, plus a sediment flush while we are in there.

3. Anode rod corrosion

Every storage hot water tank has a sacrificial anode rod inside. It is a long magnesium or aluminium rod hanging into the water from the top of the tank. It is designed to corrode instead of the tank wall.

Anode rods last 5 to 8 years. After that they are fully consumed and the tank itself starts corroding. Symptoms appear slowly: tank capacity feels reduced, water sometimes has a faint metallic smell, hot water has a yellowish tinge.

Tell-tale signs: 5 to 10 year old tank, water sometimes smells of rotten eggs, water occasionally looks discoloured.

Fix: anode rod replacement, $180 to $240. Best money you can spend on extending tank life. Most people never know it is even a thing.

4. Dip tube failure

Cold water enters the tank through a dip tube that runs down to the bottom of the tank, so cold water sits at the bottom and hot at the top. If the dip tube cracks or falls off, cold water now enters at the top – right where the outlet is. You get a brief burst of hot, then cold.

Tell-tale signs: hot water lasts 30 to 60 seconds then goes cold rapidly, regardless of how much you have used. Tank seems "fast to recover" because it is barely heating anything.

Fix: dip tube replacement, around $280 to $380. Rare but not unheard of, especially in tanks 10+ years old.

How I narrow it down

Five minutes of questions usually pins it. Age of the tank, electric or gas, off-peak or continuous, how long since it was last serviced, what the symptoms feel like exactly. After that, a single site visit confirms it.