Running Out of Hot Water: Causes and Solutions Explained

There was a time when you enjoyed an endless supply of hot water, yet now your shower turns cold unexpectedly, leaving the last bather with only a lukewarm trickle. If you notice that your access to hot water is diminishing more quickly than it used to, it indicates that something is amiss. This issue may arise from changes in household usage patterns, problems within the hot water system itself, or issues with the energy source powering the system.

This detailed guide outlines seven common reasons for hot water shortages in Queensland households. It also provides insights into how long you should expect to wait for hot water to return after it has been used up, along with practical checks you can perform before calling in a plumber.

Understanding the Main Causes of Hot Water Shortages

• An electric tank operating on an off-peak (controlled load) tariff heats water only when the electricity network activates its power supply, which can leave it cold until the next scheduled off-peak period.
• If the water remains cold the following morning, it suggests a malfunction rather than high demand.
• Frequent causes of hot water shortages include an undersized tank for the household’s needs, a malfunctioning heating element or thermostat, sediment build-up, a thermostat set too low, insufficient solar boosting, tariff limitations, or an ageing system.

What Is the Expected Wait Time for Hot Water to Come Back After Depletion?

The time you should wait primarily depends on the type of hot water system you have and its energy source.

• Electric storage tank on a standard tariff: The heating element activates immediately when the water temperature drops, allowing for quick reheating of the tank. Larger tanks with smaller elements may take longer to reach the desired temperature.
• Electric storage tank on an off-peak tariff: In Queensland, these controlled load tariffs are referred to as Tariff 31 or Tariff 33. Your electricity provider controls when power is supplied, meaning a tank that empties in the evening might not begin reheating until the next off-peak cycle.
• Gas storage tank: The burner ignites whenever the water temperature drops, enabling immediate reheating. If it fails to do this, check the pilot light for any issues.
• Gas continuous flow: These systems heat water on demand, eliminating the risk of running out. If the water turns cold, the issue likely lies with a fault, gas supply, or flow problem rather than a lack of stored hot water.
• Solar hot water: Recovery depends on sunlight availability and the efficiency of the booster. After several cloudy days, the booster typically takes on most of the workload.

According to Energy Made Easy, the Australian Government’s energy comparison service, a controlled load tariff is applicable to larger appliances like hot water systems that operate on their own circuit, with power limited to specific time slots, usually overnight and on weekends (Energy Made Easy, Understanding controlled loads). If your hot water remains cold the next morning after an off-peak period, it implies that the tank has not reheated, indicating a fault rather than excessive consumption.

For those using gas hot water systems and experiencing a lack of hot water, our guide on pilot light issues can assist you in performing essential initial checks.

1. Is Your Hot Water System Appropriately Sized for Your Household?

Hot water systems are typically sized to accommodate the household they serve. As families expand, teenagers take longer showers, and remote work increases daytime usage, a system designed for two individuals may struggle to meet the demands of a family of four.

Signs that your hot water system may be inadequate:

• Hot water runs out after just one or two consecutive showers.
• The family must coordinate shower timings to ensure the last person does not end up with cold water.
• The issue arose following an increase in household size, rather than as the system aged.

If your hot water system is functioning properly but simply lacks the required capacity, upgrading to a larger tank or a different system type will resolve the issue. Our guide to various hot water systems suitable for Brisbane and Moreton Bay homes compares options such as electric, gas, solar, and heat pump systems.

2. Are There Problems with the Heating Element or Thermostat in Your Electric Hot Water System?

An electric storage tank depends on its heating element to warm the water and its thermostat to control the heating cycle. If either of these components starts to fail, the water may heat inadequately or not at all, causing the tank to deplete more quickly than before.

Signs of a failing heating element or thermostat:

• The water is warm but does not reach the desired hot temperature.
• Hot water runs out noticeably faster than it did a few months ago.
• The safety switch trips when the hot water system is powered on.

Both the heating element and thermostat are located behind a cover on the tank and operate on mains power. Avoid attempting to open this cover yourself. A qualified plumber can evaluate both components and advise whether replacement is feasible based on the tank’s age. Schedule a hot water system inspection if you encounter any of these symptoms.

3. Is There Sediment Build-up in Your Hot Water Tank?

Over time, minerals in the water settle at the bottom of a storage tank. This sediment layer occupies space that should be filled with hot water, and in electric tanks, it can coat the heating element, impeding the heating process.

Signs of sediment build-up in the hot water tank:

• Rumbling or popping sounds coming from the tank during heating.
• Hot water depletes more quickly despite no changes in usage patterns.
• Cloudy, gritty, or rusty water coming from the taps.

During a service visit, a plumber will flush the sediment from the tank and inspect the sacrificial anode, a rod inside the tank designed to corrode and protect the tank from deterioration. Our article on hard water and hot water systems in Caboolture discusses how water quality affects a tank’s lifespan.

4. Is Your Hot Water Thermostat Set to an Inadequate Temperature?

Some individuals lower the thermostat setting to conserve energy or to avoid excessively hot water at the taps. The downside is that cooler water in the tank depletes more quickly, as less cold water mixes during showers, resulting in greater consumption of the tank’s contents.

The Queensland Government advises that stored hot water in homes must be heated to a minimum of 60°C to prevent the growth of bacteria such as Legionella. New and replacement systems must include a temperature control device to ensure that water reaches taps at a maximum of 50°C (Business Queensland, Hot water systems). Lowering the thermostat below 60°C to prevent scalding is not recommended, as the temperature control device is specifically designed for this purpose.

An improperly adjusted temperature control device can also lead to showers feeling cooler than expected. A licensed plumber can check both the tank thermostat and tempering valve to ensure they are calibrated according to Queensland regulations.

5. Is Your Solar Hot Water System Getting Enough Sunlight or Is the Booster Malfunctioning?

If you have a solar hot water system and notice a decrease in performance, this is usually linked to either weather conditions or the booster’s functionality. The system relies on its electric or gas booster during cloudy or rainy days, and in winter when sunlight is less intense.

Key indicators of issues with a solar hot water system:

• The shortage coincides with a period of overcast or rainy weather.
• The booster switch is turned off, or the booster fails to activate properly.
• The controller shows a fault indicator or error message.

Our guide to solar hot water boosters in Queensland explains how the booster operates and clarifies why every solar system requires one.

6. Are Your Off-Peak Tariffs Restricting Your Electric Hot Water System’s Reheating Time?

Many households in Queensland use electric hot water systems on Tariff 31 or Tariff 33. These tariffs offer reduced rates because the network only powers the hot water circuit during specific times. If your household consumes more hot water than the tank can replenish between these intervals, it will run out and remain cold until power is restored.

Indicators that tariff restrictions may be causing the problem:

• Hot water runs short in the evening but is available again the next morning.
• Your electricity bill includes a separate entry for a controlled load, specifically Tariff 31 or Tariff 33.
• Additional guests or extra laundry loads have pushed the tank to its limits.

Energy Matters notes that the second controlled load option is slightly more expensive than the first but provides power for a longer duration, often covering part of the day (Energy Matters, Controlled Load Tariff Explained). Your options include upgrading to a larger tank, switching to a tariff with extended supply hours, or choosing a different type of system. Your electricity retailer can confirm your current tariff.

7. Is Your Hot Water System Approaching the End of Its Lifespan?

As hot water storage tanks age, they often lose capacity due to sediment build-up and wear on components. If your hot water supply is diminishing and the tank shows signs of rust, leaks around the base, or increasing noise levels over the years, replacing the system may be more practical than ongoing repairs.

Our article on the lifespan of hot water systems offers a comprehensive overview of the typical duration for each type, while our guide on leaks from the bottom of a water heater clarifies what a leak around the tank’s base typically indicates.

Essential Checks to Perform Before Contacting a Plumber About Hot Water Shortages

A few straightforward checks can help identify the cause of hot water shortages and assist your plumber in diagnosing the issue. None of these steps require you to open the hot water system.

• Observe when the hot water runs out: Is it only in the evening, after a certain number of showers, or is it a consistent issue?
• Review your electricity bill for any mention of a controlled load, Tariff 31, or Tariff 33.
• Check the base of the tank and the relief valve pipe for any signs of dripping or pooling water.
• Listen for any rumbling or popping sounds while the tank heats up.
• If you have a solar system, ensure that the booster switch is turned on and that the controller indicates no faults.
• Locate the brand, model, and installation date on the label affixed to the side of the tank.

Common Questions Regarding Hot Water Shortages

How long does it take for hot water to return after it has run out?

The wait time varies based on the system type. Electric tanks on a standard tariff and gas storage tanks begin reheating immediately. An electric tank on Tariff 31 or Tariff 33 only reheats when the network powers the circuit, which may leave it cold until the next off-peak period. If the water remains cold the following morning, it’s best to have the system inspected.

How can I tell if I need a larger hot water system or a completely new one?

If the issue arose when your household size increased and the system otherwise operates well, it likely indicates a need for a larger system. Conversely, if the problem has developed gradually in an older tank, or if the tank shows signs of rust, leaks, or unusual noises, replacement is likely the better option.

Can I increase the size of my hot water tank?

While you cannot physically enlarge an existing hot water tank, you can replace it with a larger system. We evaluate the number of residents in the household, their hot water usage patterns, and the system’s energy source to recommend an appropriately sized tank and system type.

How long does it take to replace a hot water system?

Most hot water system replacements are completed within a single day, especially when the new system matches the type and size of the old one.

Expert Hot Water Solutions in Caboolture, Morayfield, and Moreton Bay

Creek to Coast Plumbing has proudly served homes across Caboolture, Morayfield, and the Moreton Bay region since 2012. Our licensed plumbers and gas fitters specialise in the installation and servicing of electric, gas, solar, and heat pump hot water systems. We will identify the cause of your hot water shortages, explain your options, and provide a quote before any work begins.

Contact us at 1300 793 962 or send a message to Damian or our team detailing your hot water issue and when it occurs. You can also learn more about our hot water services in Caboolture.