Under the national plumbing standard AS/NZS 3500.4—which governs heated water services to protect households from scalding while preventing bacterial growth—stored hot water in NSW must be kept at a minimum of 60°C to inhibit Legionella bacteria, while water delivered to sanitary fixtures like showers, baths, and basins is capped at 50°C. These storage and delivery temperature requirements differ because a certified tempering valve automatically blends cold water with the hot supply downstream of the cylinder.
Change the temperature only through a controller or dial that your hot water system’s manual identifies as a user control. Adjust it by one small step within the manufacturer’s approved range. Do not remove covers or alter internal electrical, gas or plumbing components.
Check the system and control
First, identify whether you have a storage or continuous-flow system from the appliance label or manual. Then check whether all hot taps are too cool. If only one outlet is affected, the issue may be at that fixture rather than the heater.
- Continuous-flow systems may have a wall-mounted digital controller intended for household use. Follow the model-specific instructions and do not override locks or temperature limits.
- Storage systems often have thermostats behind protective covers. Adjust a dial only if the manual clearly identifies it as accessible and user-operated. If you need tools or must remove a cover, stop and contact a professional licensed for that work.
Record the original setting before making an approved adjustment.
Make and check the adjustment
After increasing the setting slightly, allow the response time specified in the manual. A storage system may need to complete a heating cycle.
Check the result carefully with a suitable water thermometer rather than your hand. Keep children and people with reduced mobility or temperature sensitivity away during testing. Hotter water can cause serious scalds.
Never handle wiring, open an electrical panel, adjust internal gas controls or bypass a safety limit. Electrical, gas and regulated plumbing work must be completed by an appropriately licensed tradesperson.
Why the tap water may stay cooler
A tempering valve can limit the temperature delivered to bathroom or other personal-hygiene taps by mixing hot and cold water. Turning up the heater may therefore raise the stored-water temperature without making those outlets hotter.
Do not adjust, bypass or replace a tempering valve yourself. If there is no approved user control, the setting does not respond, temperatures become erratic or the water remains unsafe, contact our trusted Sydney hot water plumbers. Fixed Today has supported Sydney homeowners for over 15 years with honest advice, testing your water temperature on site with calibrated digital thermometers and walking you through every step of a safe, compliant repair.