Why do I only get a little bit of hot water then it goes cold?

That classic pattern on an electric system points to a failed lower heating element or thermostat. The top element heats only the top of the tank, giving a short burst before cold water comes through.

Can flushing my hot water tank help?

Yes -- draining sediment from the bottom of the tank can restore lost capacity and efficiency, and is good annual maintenance. If flushing makes little difference, the element, thermostat, or the tank itself is the issue.

Do I need a plumber to fix hot water?

Minor electric element and thermostat checks can be done by a competent person with the power isolated, but tank replacement, and any gas or solar work, must be carried out by a licensed plumber or gasfitter.

Why does my hot water run out so quickly?

Hot water running out fast usually means a failed element or thermostat, sediment, a broken dip tube, or an undersized tank. How to narrow it down.

Quick answer

Hot water running out fast usually means a failed lower heating element or thermostat (electric), a sediment build-up shrinking the tank, a broken dip tube mixing cold into the hot outlet, or simply a tank too small for the household. Test the element and thermostat first; persistent problems on a gas or solar system need a licensed plumber or gasfitter.

Skill level: All levels
Time: 4 min read
Trade: Plumbing
Updated: 14 November 2026

The short answer

A storage hot water system holds a fixed volume. If it used to last and now runs cold quickly, something has reduced either how much it heats or how much usable hot water leaves the tank.

On an electric system the most common cause is a failed lower element or thermostat -- the top element still heats the top third of the tank, so you get a short burst of hot water then cold. Sediment on the tank floor and a cracked dip tube are the next suspects.

What it depends on

Fuel type -- electric elements and thermostats are the usual fault; gas points to the thermostat or burner; solar points to the booster or a cloudy-day boost setting.

Tank age -- sediment build-up over years steadily shrinks usable capacity, and tanks over 10-12 years may simply be near end of life.

Household demand -- a system that was fine for two people can genuinely be undersized after the family grows.

Whether it is sudden or gradual -- a sudden change points to a failed part; a slow decline points to sediment or ageing.

Your next step

Electric element and thermostat testing is doable if you are competent and the power is isolated, but the connections and any gas or solar work must be done by a licensed plumber or gasfitter. If the system is more than a decade old, replacing it can be cheaper over time than repeated repairs -- and for a work premises a new unit over the write-off threshold may be a deductible business asset. Browse more plumbing guides, and if cost is the blocker see equipment and asset finance.

Frequently asked questions

Why do I only get a little bit of hot water then it goes cold?: That classic pattern on an electric system points to a failed lower heating element or thermostat. The top element heats only the top of the tank, giving a short burst before cold water comes through.
Can flushing my hot water tank help?: Yes -- draining sediment from the bottom of the tank can restore lost capacity and efficiency, and is good annual maintenance. If flushing makes little difference, the element, thermostat, or the tank itself is the issue.
Do I need a plumber to fix hot water?: Minor electric element and thermostat checks can be done by a competent person with the power isolated, but tank replacement, and any gas or solar work, must be carried out by a licensed plumber or gasfitter.

Written by Pipey, the Plumbing specialist at WA.Tools.