No hot water? What to check, and when to call

Nobody finds out the hot water’s gone at two in the afternoon with nowhere to be. It’s always a morning, usually a cold one, and usually with somebody already late standing behind you in a towel.

The good news is that a fair share of “no hot water” mornings end with a reset rather than a plumber. The table below is the quick version. Find the line that matches what you’re seeing, then read that section.

Is it every tap, or just some?

Run the hot tap in the kitchen, then the bathroom, then the laundry. If none of them run hot, the problem is the unit or its supply. If some run hot and some don’t, the unit is working and the fault is somewhere between it and the cold taps.

That one test cuts the list of causes roughly in half, and it takes about a minute.

Gas storage: is the pilot light out?

On a gas storage unit, the most common cause of no hot water is a pilot light that’s gone out. Look through the small window near the bottom of the tank. No little blue flame means no pilot.

A gust of wind down the flue can put it out. So can a short interruption to the gas supply. The relighting steps are printed on the label on the unit itself, and they differ between brands, so follow the label rather than a video of somebody else’s heater.

If it lights and stays lit, you’re done, and the water should be hot again in an hour or so. If it lights and goes out again as soon as you let go of the knob, the usual culprit is a thermocouple, the small part that tells the gas valve the pilot is burning. Replacing it is a job for a licensed gas fitter.

Electric storage: power, the breaker and off-peak

On an electric unit, start at the switchboard. Look for a breaker labelled hot water or HWS. If it’s tripped, reset it once.

If it trips again, leave it off. A breaker that won’t stay on is telling you there’s an electrical fault in the element or the wiring, and resetting it over and over just makes the same point more loudly.

If the breaker’s fine, think about when you ran out. A lot of Melbourne homes have electric units on an off-peak tariff, which only heats the tank overnight. A big day of showers, washing and a bath for the kids can empty it by evening, and it won’t recover until the off-peak period starts again. The fix is a bigger tank, or a boost switch that can heat it during the day.

If the breaker’s on, the tariff isn’t the issue and the water’s still cold by morning, the element or the thermostat has probably failed. Both can be replaced without replacing the unit.

Continuous flow: what’s the error code telling you?

A continuous flow unit heats water as it passes through, and it needs both gas and electricity to do it. So first, check that the power point it plugs into is switched on and working. It’s the simplest thing to rule out.

Then look at the controller in the kitchen or bathroom, or on the unit itself. Most show an error code when something’s wrong, and the manual for your model will say what each one means. Some codes are a reset. Others mean a part has failed.

One more thing that catches people out: these units need a minimum flow of water before they fire. A tap opened to a trickle may never trigger the burner, so try opening the hot tap fully before deciding it’s broken.

Hot in the kitchen, cold in the shower

If the kitchen runs hot and the bathroom doesn’t, look at the tempering valve. It’s a valve that mixes some cold water into the hot on its way to the bathroom, so the water reaching the shower can’t scald anyone. In Victoria, bathrooms in newer installations have to be supplied at no more than 50°C, and the tempering valve is how that happens.

Kitchens and laundries usually aren’t tempered. So when a tempering valve fails, the bathroom goes lukewarm or cold while the kitchen tap stays perfectly hot. The hot water unit is fine. The valve is the part that needs fixing.

The other possibility, if it’s only one shower, is the mixer itself. A worn cartridge in a shower mixer can stop it delivering hot water even when every other tap is fine. Both are repairs for a licensed plumber, and neither means replacing the hot water unit.

Signs the unit itself has failed

Some faults are a reset or a part. Some mean the unit has reached the end of its life. The signs of the second kind:

Signs it's time for a new unit

• Water leaking from the body of the tank, not from a valve or a pipe
• Rust-coloured hot water, when the cold runs clear
• A unit more than about ten years old that keeps needing repairs
• Rumbling or popping from the tank as it heats

A few drips from the relief valve drain while the unit heats is normal. The water expands as it heats and the valve lets a little out. A steady stream, or water pooling around the base, is not normal.

If you do need a new unit, our guide to what a hot water replacement costs in Melbourne covers the prices by system type and the Victorian rebate.

When to stop and call

Resetting a breaker and relighting a pilot are fair game. Past that, stop.

Anything connected to gas or to your water supply is licensed work in Victoria. That’s for good reason, since a hot water unit is a pressurised tank of very hot water sitting next to a gas line.

If it’s the middle of the night and water is coming out of somewhere it shouldn’t, turn the water off at the isolation valve on the cold inlet to the unit, or at the meter, and call. Our phone’s answered 24 hours a day, and emergency plumbing is what that number is for. If you’d like to know what an after-hours call-out costs first, our guide to what a plumber costs in Melbourne has the current rates.