How to Adjust a Hot Water Tempering Valve?

If your shower keeps switching from lukewarm to way too hot, chances are your tempering valve needs adjusting. The good news? It’s often a simple fix you can handle yourself.

Here’s what you need to know to adjust a tempering valve, so you can get things sorted before picking up the phone to call hot water experts in Sydney.

What Is a Tempering Valve?

A tempering valve mixes hot and cold water to give you water that’s safe to use. It keeps your taps from pumping out water hotter than 50°C, which is the maximum allowed under Australian plumbing codes (AS/NZS 3500.4).
.
What makes it important:

• Prevents burns and scalds
• Stops bacteria, like Legionella, from growing in your system
• Keeps your water consistent across showers, sinks, and baths

When Should You Adjust Your Tempering Valve?

Most of the time, your hot water tempering valve just gets on with the job. But sometimes, it needs a little adjustment.

• Your hot water feels lukewarm, not hot
• The water temperature changes randomly
• You’ve just installed a new hot water system

Is It Safe to Adjust a Tempering Valve Yourself?

In Australia, only licensed plumbers are legally permitted to carry out plumbing work on hot water systems.

If you’re making a minor, surface-level adjustment, such as turning a valve screw without disassembling or modifying the system, and you understand the risks, yes, you are technically be able to do it.

If you are unsure or if the system requires more than a small tweak, the safest and best choice is to contact a plumber. They’ll ensure everything meets Australian safety standards and operates as it should.

How to Adjust a Tempering Valve

Step 1: Turn Off the Water Supply

• Locate the isolation valve on the cold water line feeding your hot water system. This is a small tap or lever near the unit.
• Turn it clockwise to close the valve and stop the flow of water.
• This step helps avoid pressure changes while adjusting the tempering valve. It also gives you more control during testing.

Step 2: Locate and Remove the Tempering Valve Cap

• The tempering valve is a round, T-shaped, or cylindrical device installed near the outlet of your hot water unit.
• Look for a protective cap on the top or front of the valve. This shields the adjustment point.
• Use a flat-head screwdriver or your hand to gently twist or pop off the cap.

Step 3: Identify the Adjustment Mechanism

Under the cap, you’ll see the control point that allows you to adjust the mixed water temperature. This may appear as:

• A slotted screw head (flat-head type)
• A knurled dial (small, ridged knob you can turn by hand)
• A recessed hex nut that requires a specific tempering valve adjustment tool. The tool is a T-shaped or hex key-style designed to fit snugly into the nut for safe turning.

Step 4: Make Small Adjustments to the Temperature

• Use your screwdriver or adjustment tool to turn the mechanism slowly:
• Clockwise to reduce the outlet temperature or counter-clockwise to increase the outlet temperature
• Wait 30–60 seconds to allow the internal mechanism to stabilise.

Step 5: Run a Hot Tap and Check the Temperature

• Go to the hot water tap closest to the system.
• Turn on the hot tap and let it run for at least 60 seconds to ensure the water from the tank reaches the outlet.

Step 6: Finalise the Adjustment and Secure the Valve

• Once the water temperature is steady at the desired level, gently tighten the adjustment screw.
• Reattach the protective cap securely to cover the adjustment point.

Next step?

Run a few taps around the house to confirm a consistent temperature.

If everything feels even and safe, you’re good to go. If not, or if anything seems off, like continued temperature swings or dripping, it’s time to call a plumber.

Signs Your Tempering Valve Is Faulty

Not every temperature issue can be fixed with an adjustment. Some signs suggest your valve needs replacing:

• Water remains cold even after adjustment
• Sudden swings between hot and cold
• Unusual noises near the valve (banging or knocking)
• The valve is visibly leaking
• It’s over 5–8 years old

A faulty valve won’t regulate temperature properly and can put your household at risk. In that case, replacement is the safest option.

Final Thoughts

Once the temperature is steady and reliable, you can relax knowing you’ve handled it right. If you are still having issues or are not sure if the valve is faulty, that’s where Fix N Flow comes in.

Call us on 1300 319 275 or fill out our online form, and we’ll get your hot water sorted immediately. Our hot water repairs in Sydney professionals can handle adjustments, replacements, and full system checks safely.