Why Does My Hot Water Keep Running Out So Quickly? Causes & Fixes

There’s nothing worse than standing there starkers in the shower, ruining the only quiet time you get with your thoughts, when suddenly the water turns ice cold. If your hot water keeps running out too quickly, there are a few reasons why — and the cause often depends on the type of system you have. Whether it’s solar, heat pump, electric, gas storage, or instantaneous, each type of unit heats water differently, so some of these factors may or may not apply to you.

Here are five common reasons your hot water keeps cutting out — and what you can do about it.

1. Your Hot Water Unit Isn’t Big Enough

Storage hot water systems (whether gas or electric) can only store a certain amount of hot water. So, if you’re the last one in line for a shower, you’re the one getting stitched up with a cold rinse.

For large families, we usually recommend an instantaneous unit, so you’ll never have to worry about your hot water running out quickly again. Storage hot water units range from 25L up to around 400L for domestic systems, but they’re bulky and take up a lot of space. An instantaneous unit, on the other hand, sits neatly on your wall — out of sight and out of mind — just doing its thing and serving hot water on demand.

2. The Electrical Element or Burner Is Buggered

In electric storage systems, the element is basically a giant kettle heating the tank. Like everything, it has a lifespan and eventually fails.

Gas storage units use a burner at the bottom of the tank. If the flames aren’t getting hot enough, there could be a gas issue — from a faulty control valve to a thermocouple not sensing the flame. The result? Water that’s lukewarm at best, or not heating at all.

3. Hot & Cold Cross-Connection

We’ve fixed a number of these. Somewhere along the line, a handyman, DIYer, or even a plumber who wasn’t concentrating may have connected the hot line to the cold. This causes cold water to mix in, cooling everything down.

The problem here isn’t the hot water unit — it’s the cold water feeding into the hot line. We’ve also seen this happen during renovations, where taps or mixers were capped off incorrectly. If the spindles are missing or temporary caps are used, hot and cold water can mix inside the breach. The same goes for mixers left connected during a reno — with the outlet capped, the lines cross, and your whole property ends up with nothing but lukewarm water.

4. Faulty Tempering Valve

If, at this point, you’re still looking for an answer to the question, “Why does my hot water keep running out?” The culprit could be your unit’s tempering valve.

By law, domestic hot water units must have a tempering valve fitted and set to 50°C (except for some instantaneous systems that are factory-set).

Tempering valves mix hot and cold water to deliver safe tap temperatures. Over time, they can fail, reduce pressure, or clog up with sediment. That means your water either won’t get hot enough, or you’ll notice the pressure dropping as well.

5. Your Unit Is Gone & Needs Replacing

Like many things in life — including my hairline — sometimes things just get old and break down. Most hot water systems have a lifespan of 10–15 years, although I’ve seen units soldier on for nearly 30.

That said, they don’t make them like they used to. These days, it’s usually cheaper to replace an older system than to keep patching it up. A new unit comes with a 5–10 year warranty and will run far more efficiently. So, if you’re constantly calling for hot water system repair, a full replacement might be the better choice.

Time to Call a Plumber?

If your hot water keeps running out, don’t put up with it. Sometimes, it’s just a faulty part; other times, it’s a sign you need a new unit altogether. Either way, we’re here to help if you need a plumber to fix your hot water system.

At X1 Plumb, we’ve replaced and repaired hundreds of hot water units across Bayside and Melbourne. We provide free quotes and advice with no strings attached to help you find the best option for your home or business. Don’t hesitate to contact us today.