Why Would a Hot Water Heater Suddenly Stop Working?

One morning you turn on the shower, and instead of steamy water, you get ice-cold water. You check the bathroom sink, the kitchen tap, the laundry tub - all the same. No hot water. Your water heater just stopped working. It wasn’t making any noise. No warning lights. No leaks. It just… gave up. This isn’t rare. In Perth, where winters get chilly and showers are non-negotiable, a sudden loss of hot water is one of the most common - and frustrating - home emergencies.

It’s Probably Not the Power

Before you panic, check the obvious: is the power on? For electric water heaters, the problem is often simpler than you think. The heating element might be dead, but before you replace it, check the circuit breaker. A tripped breaker is the #1 reason electric water heaters stop working. Go to your switchboard, find the breaker labeled "Water Heater" or "Hot Water," and flip it off, then back on. If it trips again right away, you’ve got a short circuit - probably a faulty element or wiring issue. Don’t keep resetting it. That’s a fire risk.

For gas water heaters, the issue isn’t power - it’s gas and ignition. If your heater uses a pilot light, make sure it’s still burning. If it’s out, follow the relighting instructions on the unit. If it won’t stay lit, the thermocouple is likely bad. This little copper tube senses the flame and tells the gas valve to stay open. If it gets dirty or worn, it shuts off the gas supply. Replace it. It costs under $30 and takes 20 minutes.

Thermostat Trouble

Thermostats don’t last forever. In electric tanks, there are usually two: one for the top element and one for the bottom. If the top one fails, you might get a little hot water - just enough to fill the upper part of the tank before it cools. If the bottom one dies, you get cold water even if the top element is working. Both can fail independently.

Older thermostats are mechanical. They get sluggish. If you turn the dial up and nothing changes, that’s a red flag. Newer models have digital displays, but even those can glitch. Try resetting the thermostat. Some have a reset button (usually red) behind a small panel on the side of the tank. Press it. If the heater kicks on, you’re good. If not, the thermostat needs replacing. It’s not hard. Just turn off the power, take off the cover, unplug the wires, swap the unit, and plug it back in.

Heating Elements Burn Out

Electric water heater elements are like light bulbs - they eventually burn out. They’re designed to last 8-12 years, but hard water in Perth accelerates their death. Minerals build up on the element, making it overheat and fail faster. If you’ve had the same heater for over a decade, this is likely your issue.

How to test it? You need a multimeter. Turn off the power. Drain the tank a bit. Remove the access panels and insulation. Unhook the wires from the element. Set your multimeter to ohms. Touch the probes to the two terminals. If it reads zero or infinity, the element is dead. Replace it. Same size, same wattage. Don’t guess. A 3500W element won’t work if your tank needs a 4500W one. Also, flush the tank while you’re at it. Sediment buildup is the silent killer of elements.

Hands testing a water heater element with a multimeter as sediment drains from the tank.

Gas Burner or Ventilation Issues

If you have a gas heater and it’s not heating, the burner might be clogged. Dust, spider webs, or even rust can block the gas flow. The flame might look weak or uneven, or not light at all. Cleaning the burner requires removing the access panel and using a brush or compressed air. Don’t use water. Let it dry completely before relighting.

Another hidden issue: poor ventilation. Gas heaters need air to burn cleanly. If the flue is blocked - by bird nests, leaves, or even a collapsed chimney liner - the heater shuts down as a safety feature. Check the top of the unit where the vent pipe exits. If you see debris, clean it. If you’re not sure, call a gas fitter. Gas leaks are serious.

Pressure Relief Valve Failure

This is one of the least talked about but most dangerous issues. The pressure relief valve is there to stop your tank from exploding. If it leaks constantly or won’t shut off, it might be stuck open. That doesn’t mean the heater isn’t heating - it means the water is escaping before it can get hot. You’ll notice water pooling under the tank or dripping from the pipe on the side.

Try lifting the lever on the valve. If water shoots out and then stops when you let go, it’s working. If it keeps dripping, the valve is faulty. Replace it. It’s cheap. But if the valve keeps failing, your water pressure is too high. Install a pressure-reducing valve on the main line. Most homes in Perth run at 600 kPa - the safe max is 500 kPa. High pressure stresses the tank and valves.

Rusty water heater leaking from a faulty pressure valve, water pooling on the floor.

Sediment Buildup - The Silent Killer

Perth’s water has high mineral content. Over time, calcium and magnesium settle at the bottom of your tank. This sludge acts like insulation. The heating element can’t reach the water. The water heats slowly, then cools fast. You think it’s broken. It’s just buried.

Flushing the tank once a year can double its life. Turn off the power or gas. Shut the cold water inlet. Attach a hose to the drain valve at the bottom. Open the valve and let it run until the water runs clear. It might take 15 minutes. If it’s thick and muddy, you’ve got a problem. Do this before winter. If you haven’t done it in five years, your heater might be beyond saving.

Age Is the Real Culprit

Most water heaters last 8-12 years. If yours is 15 or older, it’s not a matter of if it will fail - it’s when. Corrosion eats away at the tank lining. Even if you fix the element or thermostat, the tank itself might be rusting from the inside. Look for rust stains on the floor, a wet spot near the bottom, or a strange metallic smell in the water. Those are signs the tank is done.

Replacing a water heater isn’t cheap - but it’s cheaper than a flooded laundry room. If your heater is over 10 years old and you’re having frequent issues, start thinking about replacement. Modern units are 20-30% more efficient. You’ll save on bills, and you won’t be stuck with cold showers in the middle of winter.

What to Do Right Now

Here’s what to do if your water heater stops working:

Check the circuit breaker (electric) or pilot light (gas).
Test the thermostat - reset it if possible.
Flush the tank if it hasn’t been done in over a year.
Listen for strange noises - popping, rumbling, hissing. Those mean sediment buildup.
Look for leaks, especially at the bottom. Rust = tank failure.
If none of that works, call a licensed plumber. Don’t mess with gas lines or electrical wiring unless you’re trained.

Don’t wait until you’re shivering in the shower. Act fast. A water heater that stops working doesn’t fix itself. And in Perth, winter doesn’t wait for you to get around to it.

Why is there no hot water but the heater is on?

If the heater is powered but you’re not getting hot water, the issue is usually a failed heating element, a bad thermostat, or heavy sediment buildup. In electric models, one of the two elements may have burned out. In gas models, the burner or thermocouple might be clogged or faulty. Flushing the tank and testing components with a multimeter can help pinpoint the problem.

Can a water heater explode if it stops working?

No - a water heater doesn’t explode because it stops working. But if it fails while still heating - especially if the pressure relief valve is stuck closed - pressure can build up dangerously. That’s why the valve is there. If you notice water leaking from the valve or hear hissing, don’t ignore it. Turn off the power or gas and call a professional immediately.

How often should I flush my water heater?

Flush your water heater at least once a year. In areas like Perth with hard water, doing it twice a year is better. Sediment buildup reduces efficiency, strains the heating elements, and shortens the tank’s life. A yearly flush can add 5-10 years to your heater’s lifespan.

Is it worth repairing an old water heater?

If your heater is over 10 years old and you’re spending more than $300 on repairs, replacement is usually the better choice. Older units are inefficient, prone to leaks, and cost more to run. A new model can cut your energy bill by 25% or more. Plus, modern units come with 10-year warranties and better safety features.

What’s the difference between electric and gas water heater failures?

Electric heaters fail because of faulty elements or thermostats - both electrical components. Gas heaters fail due to pilot light issues, thermocouple failure, clogged burners, or ventilation blockages. Gas units don’t need electricity to heat, but they do need airflow and a working ignition system. Electric units are simpler to test with a multimeter; gas units require more specialized tools and safety checks.