First: two checks anyone can do
Before diving into system-specific troubleshooting, run through these two things first — they fix more hot water problems than you'd expect.
Check the switchboard
Go to your home's main electrical switchboard (usually in the garage, laundry or outside). Look for any tripped breakers — they'll be sitting in the middle or "off" position rather than fully "on". Flip it fully off then back on. For off-peak electric hot water systems, also check the dedicated hot water circuit breaker, which is often on a separate controlled load meter.
Check the system's isolation switch
Most hot water systems have a dedicated on/off switch on the wall nearby (looks like a regular light switch). Make sure it's in the "on" position. It sounds obvious but gets knocked off more often than you'd think — especially systems in garages or utility rooms.
If neither of those fix it, work through the section below for your system type.
Electric hot water systems
Electric storage systems are the most common type in Australian homes. They heat water using one or two heating elements inside the tank and store it at 60–65°C.
Check the thermostat setting
The thermostat is usually behind a small panel on the front of the unit (you may need a screwdriver to open it). It should be set to 60–65°C. If it's lower, water won't get hot enough. If it's too high (above 70°C), a safety cutout may have tripped — see step 3.
Check if you're on off-peak tariff
Many electric hot water systems only heat water during off-peak hours (typically 10pm–7am). If you use more hot water than usual — guests staying, more showers — the tank may simply run out before it reheats. Wait until after 7am the following morning and check again. If this is a recurring problem, your tank may be undersized.
Reset the safety cutout
Electric systems have a high-temperature safety cutout (also called an ECO — Energy Cut Out). If the water overheats, this trips and cuts power to the element. Open the thermostat panel, look for a small red button labelled "reset" or "ECO reset" and press it firmly. You should hear a click. If it trips again shortly after, the thermostat or element needs replacing — call a plumber.
Check for a failed heating element
Electric systems have one or two elements. If you're getting lukewarm water but not hot, the upper element has likely failed (it heats the top of the tank first). If you're getting no hot water at all, both may have failed or there's a wiring issue. Either way, element replacement requires a licensed electrician — don't attempt it yourself.
Gas hot water systems
Gas systems — both storage and continuous flow (instantaneous) — are reliable but have a few specific things to check when they stop working.
Check the pilot light (storage systems)
Older gas storage systems have a standing pilot light that can blow out. Look for a small viewing window near the base of the unit — if you can't see a small blue flame, the pilot is out. Most units have relighting instructions printed on a label on the unit. In brief: turn the gas valve to "pilot", press and hold the reset button, ignite with a long lighter, hold for 30–60 seconds, then turn to "on". If it won't stay lit, the thermocouple needs replacing.
Check the gas supply
Make sure your gas is on — check other gas appliances like the cooktop. If none of your gas appliances work, contact your gas provider. If only the hot water system isn't working, the gas isolation valve (usually a lever next to the unit) may have been turned off accidentally. The valve is open when the lever is parallel to the pipe.
Check the error code (continuous flow systems)
Modern continuous flow systems (Rinnai, Rheem, Bosch, etc.) display error codes on a small screen when something goes wrong. Common codes: Error 11 — no ignition (check gas supply and pilot); Error 12 — flame failure during operation; Error 51 — inlet solenoid valve issue. Look up your model's error code list in the manual or manufacturer website for the specific fix.
Check the inlet filter (continuous flow)
Continuous flow systems have a small mesh filter on the cold water inlet. If it's clogged with sediment, water flow slows and the unit won't ignite (it needs a minimum flow rate to fire up). Turn off the water supply, unscrew the inlet filter housing, remove the mesh screen, rinse it under a tap and replace. This fixes more "no hot water" problems on continuous flow systems than you'd expect.
Solar hot water systems
Solar systems are more complex because they have two heat sources — the solar collectors on the roof and an electric or gas booster. "No hot water" can come from either side.
Check the booster first
The booster (electric or gas) is what heats the water when there's not enough sun. Check the booster's power supply or gas first — the same checks as the electric and gas sections above apply here. Most solar hot water failures in winter are simply the booster not working rather than anything wrong with the solar collectors.
Check the controller display
Solar systems have a controller (usually mounted inside the house, often in the laundry). It shows the tank temperature and may display error codes. If the tank temperature is below 45°C, the solar isn't collecting or the booster isn't firing. An error code like "FROST" means the frost protection valve has activated — this is normal after a very cold night and usually resolves itself.
Check the tempering valve
A tempering (mixing) valve blends cold water into the hot to deliver a safe temperature at the tap (usually 50°C). If this valve fails, you may get water that's either scalding hot or barely warm. The tempering valve is typically at the base of the tank. If you're getting very hot water at some times and lukewarm at others, the tempering valve is the likely culprit — it needs replacing by a plumber.
Check the roof collectors (visual only)
From the ground, look at the solar panels on your roof. Are they visibly damaged, dirty or shaded by a new tree or structure? A thick layer of dirt or bird droppings can significantly reduce efficiency. Solar panels can be professionally cleaned — don't attempt to climb on the roof yourself.
Symptoms and likely causes at a glance
When to replace rather than repair
Sometimes the most cost-effective answer is a new system. Here are the typical lifespans of each system type — if yours is approaching these ages and breaking down, replacement usually makes more financial sense than continued repairs.
When to call a plumber
Stop troubleshooting and call a licensed plumber if:
- You smell gas near the unit
- Water is leaking continuously from the tank base (tank has failed)
- The temperature/pressure relief (TPR) valve keeps dripping or running
- The system is making loud banging, popping or rumbling noises
- You've reset the safety cutout and it trips again within a day
- The pilot light won't stay lit after three attempts
- The water is discoloured rust-brown or smells of sulphur (rotten eggs)
- The system is over 10 years old and you've already had one repair
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