Posted by David MacKenzie, Friday 19th June, 2026

A shower usually keeps going hot and cold because the balance between hot water, cold water and pressure is being interrupted.

A shower that suddenly turns cold, then hot again, is more than just annoying. It can make the shower uncomfortable, unpredictable, and, in some cases, unsafe if the temperature spikes too high.

Sometimes the cause is simple, such as another tap being used at the same time. Other times, the problem points to a worn mixer, a tempering valve issue, a hot water service problem or pressure changes in the plumbing.

In this article, David looks at some of the most common shower plumbing issues we fix on an almost daily basis, and how to deal with them.

Shower Temperature Change Problems at a Glance

A shower temperature problem can show up in a few different ways. You might notice:

• The shower suddenly turns cold
• The shower suddenly becomes too hot
• The temperature keeps moving up and down
• The water starts warm, then fades cold
• The shower changes temperature when another tap is used
• The temperature is hard to control at the mixer
• The shower works normally some days, then plays up on others
• The problem is worse when other appliances are running

The pattern matters. A shower that changes temperature when someone turns on another tap may have a different issue from a shower that goes hot and cold even when no other water is being used.

Why the Shower Changes Temperature When Another Tap Is Used

If your shower goes cold when someone turns on the kitchen tap, flushes a toilet or starts the washing machine, the issue may be a pressure balance.

A shower relies on a steady mix of hot and cold water. If another fixture suddenly changes the flow or pressure, the shower may lose part of that balance. This can make the water feel colder, hotter or unstable.

This is more noticeable in homes with older plumbing, older mixers, pressure limitations or systems that do not manage changes well.

A one-off temperature change is not always a major concern. But if the shower becomes unpredictable whenever another fixture is used, the plumbing may need checking.

Mixer Cartridge Problems

Modern mixer showers use an internal cartridge to control water flow and temperature. If the cartridge wears out, blocks or becomes stiff, the shower may struggle to hold a steady temperature. A mixer problem is more likely if:

• The handle is stiff or loose
• The temperature is hard to adjust
• The shower drips after use
• The water does not shut off cleanly
• The shower alternates between hot and cold
• Small handle movements cause large temperature changes

This can overlap with other issues, such as low pressure or dripping, because the mixer sits at the centre of flow and temperature control.

Tempering Valve Issues

A tempering valve helps control the temperature of delivered hot water. If it is faulty, restricted or not working properly, the shower may not receive hot water consistently.

This can cause the shower to feel too cool, fluctuate in temperature or lose hot water pressure.

Tempering valve issues are not a DIY repair. If the shower keeps changing temperature and the problem seems linked to the hot water supply, a licensed plumber should inspect it.

Hot Water System Struggling to Keep Up

If the shower starts hot but gradually goes cold, the hot water system may be struggling to keep up with demand.

This can happen if:

• The hot water unit is undersized
• The system is ageing
• Several people are showering close together
• Other hot water appliances are being used
• The system has a fault
• Recovery time is slow

If the whole home runs out of hot water, the issue may be with the hot water service rather than the shower itself. If only the shower changes temperature, the issue may be more localised. If you suspect it’s your hot water system, we can inspect it and, if necessary, repair your hot water system for you.

Apartment and Shared Hot Water Issues

In apartments, townhouses or buildings with shared hot water infrastructure, temperature changes may not always be caused by the shower alone.

The issue may relate to:

• Centralised hot water systems
• Pressure changes in the building
• Shared risers
• Building maintenance issues
• Other residents using water
• Limits in older apartment plumbing

If you live in an apartment and the problem affects other residents or happens at peak times, it may be worth checking with building management as well as a local shower plumber.

Can You Fix a Shower Temperature Problem Yourself?

You can safely do some basic checks, but most shower temperature issues are not true DIY repairs.

Start by noticing when the temperature changes. Does it happen when another tap is used? Does it happen when the washing machine or dishwasher runs? Does the hot water fade slowly, or does it jump suddenly between hot and cold?

Also check whether other taps in the home have stable hot water. If the kitchen and bathroom basin are also inconsistent, the issue may be with the hot water system or broader plumbing.

These checks help narrow down the cause, but you should not attempt to repair mixers, tempering valves, hot water systems or internal plumbing unless you are qualified.

When Should You Call a Plumber?

Call a local plumber if the shower keeps changing temperature and the cause is not obvious.

You should also get help if:

• The water suddenly becomes too hot
• The shower switches between hot and cold without warning
• The issue happens even when no other fixtures are being used
• Hot water pressure is weak
• The mixer is stiff, loose or leaking
• The problem is getting worse
• Other taps also have inconsistent hot water
• The shower is difficult to control safely

A plumber can check whether the issue is caused by pressure imbalance, the mixer cartridge, tempering valve, hot water supply, pipework or another system fault.

How Much Does It Cost to Fix a Shower That Keeps Going Hot and Cold?

The cost to fix a shower that keeps going hot and cold depends on whether the issue is caused by normal pressure changes, the shower mixer, a tempering valve, the hot water system or shared building plumbing.

For a standard plumbing visit in Melbourne, expect a call-out or service fee plus labour. Published 2026 Melbourne plumbing guides commonly list call-out fees around $80–$250, with standard hourly rates around $100–$180 per hour.

Typical costs are:

• Basic inspection or diagnosis: around $150–$300
• Minor adjustment or simple fitting issue: around $150–$350
• Mixer cartridge replacement: around $250–$600
• Tempering valve repair or replacement: around $300–$700+
• Hot water system diagnosis: around $200–$500+
• Hot water system repair: often $300–$1,000+
• Apartment, access or shared hot water issue: often $500–$1,500+, depending on the cause and building setup

The lower end usually applies when the issue is easy to diagnose or linked to a simple fixture problem. Costs increase when the shower needs a new cartridge, the tempering valve is faulty, the hot water unit needs repair, or the issue involves shared apartment infrastructure.

Related Shower Problems

If the hot water side is weak, read:
Why Is the Hot Water Pressure Weak in My Shower?

If the shower has no hot water at all, read:
Why Is There No Hot Water in My Shower?

If the mixer is stiff, loose or hard to control, read:
Why Is My Shower Mixer Hard to Turn?

If the overall flow is weak, read:
Why Is My Shower Losing Water Pressure?

Need Help with a Shower That Keeps Going Hot and Cold in Melbourne?

If your shower keeps changing temperature, DMACK Plumbing can help work out whether the issue is coming from the mixer, tempering valve, hot water supply, pressure balance or wider plumbing.

Whether the water suddenly turns cold, becomes too hot, or will not stay at a comfortable temperature, our team can inspect the problem and recommend the right repair.

Contact Dmac Plumbing for help with shower temperature problems in Melbourne.