Water Temperature Fluctuation in Tapware: Why Does it Happen?

There’s nothing worse than being blasted by a sudden burst of icy cold — or scalding hot — water mid-shower. Unfortunately, temperature fluctuations are a common frustration in homes across Australia. While a mid-winter cold shock is unpleasant, an unexpected surge of hot water can be dangerous.

These temperature swings aren’t something you just have to live with. Once you understand what’s causing the problem, you can take the proper steps to bring consistency (and comfort) back to your water flow.

Common causes of water temperature fluctuation

Water temperature fluctuations usually come up because of problems with your water heater. However, if the heater is new, it could be a plumbing issue. Here are some scenarios that could be causing your headache:

Electric hot water systems

Electric systems need a minimum water flow to kick in and heat the water. If the hot tap isn’t turned on fully, the heating element may not activate. Opening the cold tap can then overpower the system.

Gas hot water systems

Gas systems are trickier. When a gas hot water unit is added, the gas fitter should check that your existing pipes can deliver enough pressure for it to work correctly. If they skip this step or get it wrong, the unit may struggle to maintain a steady temperature. Issues may also arise if your system is overdue for servicing.

Higher-capacity systems (20L or 26L per minute) are more likely to run into this issue, but it can also happen with smaller units (12L or 16L).

Water inefficient tapware

If your hot water runs out halfway through your shower, your tapware may be draining your heater too quickly. Water-inefficient taps and showers can drain at 12–16 litres/minute. Upgrading to a larger unit will not help if your tapware is poor quality.

Old plumbing

Sometimes, the real issue is in the walls. Many homes have a ‘trunk and branch’ plumbing setup. Think of it like a tree, with a main pipe (the trunk) and smaller pipes (branches) running off to each fixture.

If those smaller pipes are too narrow, turning on a tap elsewhere can steal pressure from your shower.

Faulty mixing valves

Pressure-balancing or thermostatic mixing valves regulate water temperature. They adjust to fluctuations in water pressure to keep things stable. But if yours is faulty, even a slight pressure change, like someone flushing the toilet, can impact water temperature.

How to fix water temperature fluctuations

Let’s look at what you can do yourself and when it’s best to hand things over to the pros.

DIY tips

Start by turning the hot tap all the way for maximum hot water flow. Give it a few seconds to reach the shower head, then slowly introduce cold water until the temperature is just right.

If the above doesn't help, try the following:

Turn off appliances

Turn off heavy water-using appliances like dishwashers and washing machines. These appliances can pull hot water from the same supply, creating sudden pressure drops.

Inspect the heater thermostat

Find your heater’s thermostat and ensure it’s set to a suitable temperature. Around 60°C is recommended for safe and effective heating.

Call a professional

If you’ve tried basic troubleshooting and the issue keeps resurfacing, it could point to a more serious underlying fault. Don’t attempt to DIY beyond the basics. When it comes to gas or plumbing, safety always comes first. Reach out for help when:

You suspect a gas supply issue: A licensed gas fitter can safely test and fix the gas pressure issues.
The pilot light won’t stay on: The pilot light in older gas heaters is a small, continuous flame that ignites the main gas burner when the thermostat calls for heat. A weak or flickering pilot light needs a professional to fix it.
There’s a faulty tempering valve: Tempering valves regulate hot water temperature and prevent scalding. If one is worn out or not working properly, a plumber can repair or replace it safely.
Your hot water system needs replacement: An expert is a must if you want to replace an undersized or outdated system.

Choosing tapware to minimise fluctuations

Taps that are stuck, don’t open fully or are water-inefficient can also contribute to temperature fluctuations. Investing in tapware with a high Water Efficiency Labelling and Standards (WELS) rating.

WELS ratings of three stars or higher indicate they have been independently tested to give the best possible flow control. They reduce the rate at which hot water is used and help to maintain a stable temperature.

Tapware that fits your budget

At Yabby, we design tapware with both performance and aesthetics in mind. Our tapware is available in quality finishes like Antique Brass, Brushed Brass, Warm Brushed Nickel, Gunmetal, Matte Black and Chrome.

With us, you get better flow and temperature control and long-lasting taps. Browse our bathroom, kitchen and laundry ranges to find fixtures that you can rely on.