When an electric storage hot water system suddenly stops producing hot water, it is easy to assume the entire unit has failed. Sometimes, however, the problem is a smaller component inside the system.
We recently attended a no-hot-water call where the storage tank was still filling normally, but the water was not heating. After testing the system, the issue was traced to a faulty thermostat.
Identifying the actual fault meant the problem could be addressed without automatically replacing the entire hot water system.
What does a hot water thermostat do?
In an electric storage hot water system, the thermostat monitors the temperature of the water inside the tank.
When the water temperature falls below the thermostat’s set point, the thermostat allows power to reach the heating element. Once the water reaches the required temperature, it switches the element off again.
If the thermostat fails and no longer allows the element to operate, the tank can remain full while the water inside stays cold.
Signs of a possible thermostat problem
A faulty thermostat can produce several different symptoms, including:
- No hot water even after the system has had enough time to heat
- Water that only reaches a lukewarm temperature
- Hot water temperatures that change unexpectedly
- A system that appears to have power but does not heat
- The high-temperature safety cut-out repeatedly operating
These symptoms do not necessarily prove that the thermostat has failed. A damaged heating element, electrical supply problem, off-peak timing issue or faulty tempering valve can produce similar results.
That is why the system needs to be properly tested rather than diagnosed from the symptom alone.
Why proper hot water fault finding matters
A no-hot-water call should not automatically result in a recommendation to replace the entire system. The first step is working through the heating process and establishing exactly where it has stopped.
Depending on the system and the symptoms, this may involve checking:
- Whether power is reaching the hot water system
- Whether an off-peak supply or timer is affecting the heating cycle
- The operation of the thermostat and safety cut-out
- The condition of the heating element
- The tempering valve if the water is warm but not properly hot
- The age and overall condition of the storage tank
This separates a repairable component fault from a broader system failure.
If the tank is sound and the rest of the system remains in reasonable condition, replacing a failed thermostat may be the sensible option. If the unit is old, leaking, badly corroded or experiencing multiple faults, replacement may provide better long-term value.
What can homeowners safely check?
You can check whether the rest of the property has power and visually inspect the switchboard for a tripped hot water circuit breaker.
If the breaker has tripped, do not repeatedly reset it. A recurring trip can indicate an electrical fault that requires professional testing.
If your system uses an off-peak electricity tariff, it may only reheat during a scheduled supply period. If the household has used all the stored hot water, you may need to wait for the next heating cycle.
Do not remove the electrical access cover or attempt to adjust or replace the thermostat yourself. The thermostat, element and internal wiring involve mains electricity and must be handled by an appropriately licensed professional.
Does a faulty thermostat mean the system needs replacing?
Not necessarily.
A failed thermostat is normally replaced rather than repaired. On a relatively sound hot water unit, installing a replacement thermostat may restore normal operation without the cost of replacing the complete system.
The condition of the tank still needs to be considered. Putting new components into an older unit that is already corroded, leaking or developing other problems may only delay an inevitable replacement.
A proper assessment should give you a clear explanation of both options, including whether the repair is likely to provide reasonable value.
No hot water in North Lakes or Moreton Bay?
Losing hot water is disruptive, but it does not always mean the entire system has failed. Proper fault finding can identify whether the problem is the thermostat, heating element, power supply, tempering valve or the unit itself.
RJT Plumbing & Gas provides hot water fault finding, repairs and replacements throughout North Lakes, Moreton Bay and surrounding North Brisbane areas.
Has your hot water suddenly stopped working? Contact RJT Plumbing & Gas or call 0417 860 064 to arrange an assessment.
Frequently Asked Questions
Can a faulty thermostat cause no hot water?
Yes. In an electric storage system, a failed thermostat may prevent power from reaching the heating element. The tank can remain full while the water inside stays cold.
How do I know whether the thermostat or heating element has failed?
The symptoms can be very similar. The thermostat, heating element and electrical supply need to be tested to identify which part of the heating circuit has failed.
Can I reset the hot water thermostat myself?
You should not remove the electrical access cover or work on the thermostat yourself. These components involve mains electricity and should be inspected by an appropriately licensed professional.
Does a thermostat fault mean I need a new hot water system?
Not necessarily. If the tank and other components remain in good condition, replacing the thermostat may restore normal operation. Replacement may be more sensible when the unit is old, leaking, corroded or experiencing multiple faults.
Why is my hot water only lukewarm?
Lukewarm water can be caused by a thermostat or element problem, heavy recent hot water use, an off-peak heating cycle or a faulty tempering valve. The system needs to be tested to identify the cause.
