Running Out of Hot Water: Causes and Solutions Explained

You once enjoyed a plentiful supply of hot water, but now your showers may turn unexpectedly cold, leaving the last bather with only a lukewarm trickle. If you notice that your access to hot water is diminishing at a faster rate than before, it indicates potential underlying issues. This situation can arise from changes in household usage patterns, problems within the hot water system itself, or issues with the energy source that powers the system.

This detailed guide outlines seven prevalent causes of hot water shortages in Queensland households. It also provides insights into how long you might need to wait for hot water to replenish after it has been used up, along with practical checks you can carry out before contacting a plumber.

Primary Reasons for Insufficient Hot Water Supply

• An electric tank operating on an off-peak (controlled load) tariff heats water only during designated power supply periods, potentially leaving it cold until the next off-peak cycle.
• If the water remains cold the following morning, it suggests a malfunction rather than merely high demand.
• Common factors contributing to hot water shortages include an inadequately sized tank for the household’s requirements, a malfunctioning heating element or thermostat, sediment build-up, a thermostat set too low, inadequate solar boosting, tariff restrictions, or an ageing system.

What Is the Expected Waiting Time for Hot Water to Replenish After Use?

The time you should wait for hot water to return depends significantly 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, enabling prompt reheating. Larger tanks coupled 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 known as Tariff 31 or Tariff 33. Your electricity provider determines when power is supplied, meaning a tank that runs out in the evening may not start reheating until the next off-peak cycle.
• Gas storage tank: the burner ignites whenever the water temperature decreases, facilitating immediate reheating. If this does not occur, 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 depletion of stored hot water.
• Solar hot water: recovery is dependent on sunlight availability and the efficiency of the booster. After several cloudy days, the booster generally takes on most of the workload.

According to Energy Made Easy, the Australian Government’s energy comparison service, a controlled load tariff applies to large appliances like hot water systems that operate on their own circuit, with power limited to specific time slots, typically 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 indicates that the tank has not reheated, pointing to a fault rather than excessive usage.

For those with gas hot water systems experiencing a lack of hot water, refer to our guide on pilot light issues for assistance with initial checks.

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

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

Indicators that your hot water system may be too small:

• Hot water runs out after just one or two consecutive showers.
• The family needs to coordinate shower timings to prevent the last person from getting cold water.
• The issue arose following an increase in household size, rather than as the system aged.

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

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

An electric storage tank relies on its heating element to heat the water and its thermostat to regulate the heating cycle. If either of these components begins to malfunction, the water may heat inadequately or not at all, causing the tank to empty more quickly than before.

Signs of a failing heating element or thermostat:

• The water is warm but fails to reach the desired hot temperature.
• Hot water runs out noticeably sooner 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 a viable option based on the tank’s age. Schedule a hot water system inspection if you observe any of these symptoms.

3. Has Sediment Built Up in Your Hot Water Tank?

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

Signs of sediment accumulation in the hot water tank:

• Rumbling or popping noises emanating from the tank during heating.
• Hot water depletes faster despite no changes in consumption 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 impacts a tank’s lifespan.

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

Some people lower the thermostat setting to save energy or to prevent 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 feature a temperature control device to ensure that water reaches taps at no more than 50°C (Business Queensland, Hot water systems). Lowering the thermostat below 60°C to avoid scalding is not advisable, as the temperature control device is specifically designed to prevent this issue.

An improperly calibrated temperature control device can also cause showers to feel cooler than expected. A licensed plumber can check both the tank thermostat and tempering valve to ensure they are set in accordance with Queensland regulations.

5. Is Your Solar Hot Water System Getting Enough Sunlight or Is the Booster Not Functioning?

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

Key indicators of potential issues with a solar hot water system:

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

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

6. Does Your Off-Peak Tariff Restrict When Your Electric Hot Water System Can Reheat?

Many Queensland households utilise electric hot water systems on Tariff 31 or Tariff 33. These tariffs offer reduced rates because the network powers the hot water circuit only 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.

Signs that tariff restrictions might be the issue:

• 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 increased laundry loads have pushed the tank to its limits.

Energy Matters notes that the second controlled load option is slightly pricier 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 selecting 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 dwindling and the tank exhibits 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 provides a detailed overview of the average duration for each type, while our guide on leaks from the bottom of a water heater explains what a leak around the tank’s base typically signifies.

Essential Checks 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 problem. None of these steps require you to open the hot water system.

• Track when the hot water runs out: Is it only in the evening, after a certain number of showers, or is it a persistent issue?
• Review your electricity bill for any mention of a controlled load, Tariff 31, or Tariff 33.
• Inspect 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.
• If you have a solar system, ensure that the booster switch is activated 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

What is the typical wait time for hot water to return after it runs 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 could leave it cold until the next off-peak period. If the water remains cold the next morning, it’s wise to have the system inspected.

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

If the issue arose when your household size increased and the system otherwise works 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 more prudent option.

Is it feasible to 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 will assess 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 type of system.

How long does it typically 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 for Caboolture, Morayfield, and Moreton Bay Areas

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 commences.

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.