Why Am I Running Out of Hot Water So Fast? Seven Causes and How Long to Wait for It to Come Back

You used to have plenty of hot water. Now the shower turns cold halfway through, or the last person in the house gets a lukewarm trickle. When you keep running out of hot water faster than you used to, something has changed: in the household, in the hot water system itself or in the way the system is powered.

This guide covers seven common causes of a hot water shortage in Queensland homes, how long you should expect to wait for hot water to come back after it runs out, and the checks you can do yourself before you book a plumber.

Quick Answers About Running Out of Hot Water

• An electric tank on an off-peak (controlled load) tariff only reheats when the network switches its power on, so it may stay cold until the next off-peak period.
• Water that is still cold the next morning points to a fault, not heavy use.
• The usual causes are a tank too small for the household, a failing element or thermostat, sediment, a low thermostat setting, a weak solar booster, tariff limits or an ageing system.

How Long Should You Wait for Hot Water to Come Back After It Runs Out?

How long you wait depends on the type of hot water system you have and how it gets its power.

• Electric storage tank on a standard tariff: the element switches on as soon as the water temperature drops, so the tank starts reheating straight away. A bigger tank with a smaller element takes longer to recover.
• Electric storage tank on an off-peak tariff: in Queensland these controlled load tariffs are called Tariff 31 or Tariff 33. Your electricity network decides when the circuit has power, so a tank emptied in the evening may not reheat until the next off-peak period.
• Gas storage tank: the burner lights whenever the water cools, so the tank starts reheating straight away. If it never comes back, check the pilot light.
• Gas continuous flow: these units heat water as it passes through and have no tank to empty. If the water goes cold, the cause is a fault, the gas supply or a flow problem rather than a shortage of stored hot water.
• Solar hot water: recovery depends on the sun and on the booster. After a run of cloudy days, the booster does most of the work.

Energy Made Easy, the Australian Government’s energy comparison service, explains that a controlled load tariff applies to a large appliance such as a hot water system on its own circuit and that its power is restricted to set periods, generally overnight and on weekends (Energy Made Easy, Understanding controlled loads). If your hot water is still cold the next morning after an off-peak period, the tank has not reheated at all, and that usually means a fault rather than heavy use.

If you have a gas hot water system and the hot water does not come back, our guide to gas hot water pilot light problems explains what to check first.

1. Your Hot Water System Is Too Small for Your Household

A hot water system is sized for the household it was installed for. Families grow, teenagers take longer showers, and working from home adds more daytime use. A tank that was right for two people often can’t keep up with four.

Signs the hot water system is too small:

• Hot water runs out after one or two showers in a row
• The family staggers showers to avoid the last one going cold
• The problem started when the household grew, not when the system aged

If the hot water system is working properly but simply holds too little, a larger tank or a different type of system is the fix. Our guide to the types of hot water systems for Brisbane and Moreton Bay homes compares electric, gas, solar and heat pump options.

2. The Heating Element or Thermostat in Your Electric Hot Water System Is Failing

An electric storage tank relies on its element to heat the water and on its thermostat to switch the element on and off. When either part starts to fail, the water heats only partly or not at all, and the tank seems to empty much faster than it used to.

Symptoms of a failing element or thermostat:

• The water is warm but never properly hot
• Hot water runs out much sooner than it did a few months ago
• The safety switch trips when the hot water system is on

The element and thermostat sit behind a cover on the tank and run on mains power, so don’t open the cover yourself. A licensed plumber can test both parts and tell you whether replacing them makes sense for the age of the tank. Book a hot water system check if you notice these symptoms.

3. Sediment Has Built Up Inside the Hot Water Tank

Minerals in the water settle at the bottom of a storage tank over the years. The layer of sediment takes up space that should hold hot water, and in an electric tank it can coat the element so the water heats more slowly.

Signs of sediment in the hot water tank:

• Rumbling or popping noises from the tank while it heats
• Hot water running out sooner even though nothing else has changed
• Cloudy, gritty or rusty-looking hot water at the taps

During a service, a plumber flushes the sediment out of the tank and checks the sacrificial anode, the rod inside the tank that corrodes so the tank itself does not. Our article on hard water and hot water systems in Caboolture explains how water quality affects the life of a tank.

4. The Hot Water Thermostat Is Set Too Low

Some people turn the thermostat down to save power or to stop the taps getting too hot. The trouble is that cooler stored water runs out faster, because you mix in less cold water at the shower and use more of the tank’s contents.

The Queensland Government’s guidance on hot water systems says that stored hot water in a home must be heated to at least 60°C to prevent the growth of bacteria such as Legionella, and that a temperature control device must be fitted to new and replacement systems so the water reaches the taps at no more than 50°C (Business Queensland, Hot water systems). Turning the tank thermostat below 60°C to protect against scalds is the wrong fix, because the temperature control device is there to do that job.

A temperature control device that is out of adjustment can also make the shower feel cooler than it should. A licensed plumber can check the tank thermostat and the tempering valve together and set both to meet the Queensland requirements.

5. Your Solar Hot Water System Is Not Getting Enough Sun or the Booster Has Stopped

If you have solar hot water and you suddenly start running out, the weather or the booster is usually involved. A solar hot water system relies on its electric or gas booster on cloudy and rainy days, and in winter when the sun is lower.

Things to look for on a solar hot water system:

• The shortage started after a run of cloudy or rainy weather
• The booster switch is off, or the booster does not seem to come on
• The controller shows a fault light or error code

Our guide to solar hot water boosters in Queensland explains how the booster works and why every solar system needs one.

6. An Off-Peak Tariff Limits When Your Electric Hot Water System Can Reheat

Many Queensland homes run their electric hot water on Tariff 31 or Tariff 33. These tariffs are cheaper because the network only powers the hot water circuit at certain times. If the household uses more hot water than the tank holds between those times, it runs out and stays cold until the power comes back on.

Signs that the tariff is the cause:

• Hot water runs short in the evening but is fine the next morning
• Your electricity bill shows a separate line for a controlled load, Tariff 31 or Tariff 33
• Extra guests or extra loads of washing tip the tank over the edge

Energy Matters explains that the second controlled load option costs a little more than the first but gives the circuit power for longer, often including part of the day (Energy Matters, Controlled Load Tariff Explained). Your choices are a larger tank, a tariff with longer supply hours or a different type of system. Your electricity retailer can confirm which tariff you are on.

7. Your Hot Water System Is Near the End of Its Life

An older storage tank loses capacity as sediment builds up and its parts wear out. When the hot water runs short and the tank is also rusting, weeping around the base or making more noise each year, a replacement often makes more sense than another round of new parts.

Our article on how long a hot water system lasts covers the typical life of each system type, and our guide to a water heater leaking from the bottom explains what a leak around the base of the tank usually means.

What You Can Check Before Calling a Plumber About Running Out of Hot Water

A few simple checks will help you work out the cause, and they help your plumber too. None of them involve opening the hot water system.

• Note when the hot water runs out: in the evening only, after a certain number of showers, or all the time
• Check your electricity bill for a controlled load, Tariff 31 or Tariff 33
• Look at the base of the tank and the relief valve pipe for water that keeps dripping or pooling
• Listen for rumbling or popping while the tank heats
• On a solar system, check that the booster switch is on and the controller shows no fault
• Find the brand, model and installation date on the label on the side of the tank

Frequently Asked Questions About Running Out of Hot Water

How long does it take for hot water to come back after it runs out?

It depends on the system. Electric tanks on a standard tariff and gas storage tanks start reheating straight away. An electric tank on Tariff 31 or Tariff 33 reheats only when the network powers the circuit, so it can stay cold until the next off-peak period. If the water is still cold the next morning, have the system checked.

How do I know if I need a bigger hot water system or a new one?

If the shortage started when your household grew and the system otherwise works well, you probably need a bigger system. If the shortage came on gradually in an older tank, or the tank shows rust, leaks or noise, a replacement is more likely to be the answer.

Can I increase the size of my hot water tank?

An existing hot water tank cannot be made bigger, but it can be replaced with a larger system. We look at how many people live in the home, how they use hot water and how the system is powered, and then recommend a tank size and system type to suit.

How long does a hot water system replacement take?

Most hot water system replacements are finished on the day of the visit, especially when the new system is the same type and size as the old one.

Hot Water Help in Caboolture, Morayfield and Moreton Bay

Creek to Coast Plumbing has looked after homes across Caboolture, Morayfield and the Moreton Bay region since 2012. Our licensed plumbers and gas fitters install and service electric, gas, solar and heat pump hot water systems. We’ll find out why the hot water is running out, explain the options and give you a quote before any work starts.

Call 1300 793 962 or send us a message and tell Damian or the team what the hot water is doing and when it runs out. You can also read more about our hot water services in Caboolture.