Why do I smell gas when I turn on the shower?

This is one of the more common calls we get, and it often ends the same way. We went out to a house in West Auckland recently where the tenant could smell gas every time they had a shower. Nothing else in the house set it off. No smell at the cooktop, no smell overnight, just the shower.

The house had a Rinnai Infinity continuous flow heater mounted on the outside wall, and the bathroom window sat right beside it. Every time someone opened the hot tap, the heater fired up, and the small puff of gas smell you get at the moment of ignition drifted straight back in through the window.

That is the unit doing its job. A continuous flow heater does not store hot water in a cylinder. It sits idle until you open a hot tap, then it lights the burner and heats the water as it passes through. That instant of lighting is where the smell comes from, and it lasts a few seconds. Because the flue outlet is usually at head height on an exterior wall, anything nearby can catch it: a bathroom window, a laundry door, a bedroom window above.

Is that smell a problem?

If it only happens when someone turns on hot water, only lasts a few seconds, and only shows up near the heater, it is very likely normal ignition. It does not mean the appliance is faulty and it does not mean you have a leak.

Normal does not mean you have to put up with it, though. The fix is usually about airflow rather than gas work. Keeping that particular window shut while someone showers is the simplest thing to try. If the unit really is sitting too close to a window or an air intake, a gasfitter can look at whether the flue can be extended or the unit shifted.

What can I check myself before ringing anyone?

Gas has no smell of its own. The rotten egg odour is added on purpose so that people notice tiny amounts, which means a strong smell does not automatically mean a large leak. What matters more is the pattern.

Three things are worth noticing, and they take no tools at all.

When does it happen? If the smell only appears while hot water is running or while the cooktop is lit, that points at normal burner behaviour. If it appears at times when nobody is using gas at all, that is a different story.

Try an early morning check. LPG is heavier than air, so it settles low and pools overnight in still conditions. Go outside first thing, before anyone has used hot water, and have a smell down low near the bottles and around the base of the heater. Ignition smell will not be there at that hour. A real leak usually will be, and it tends to be obvious rather than subtle.

Where is it coming from? Outside near the heater or the bottles is one thing. Inside the house, especially around a cooktop, is another.

If you can answer those three, you have given your gasfitter most of what they need before they even arrive.

What if it does not fit that pattern?

Stop using the appliance and ring a gasfitter. That is the whole answer.

While you are waiting, do not create any source of ignition. No lighters or matches, no smoking, and leave light switches and appliance switches alone rather than flicking them on or off. Open windows and doors so the area airs out. If the smell is strong, get everyone out of the house first and make the call from outside.

An indoor gas smell from a cooktop deserves particular care because there is no outside air to carry it away. Turn the appliance off, stop using it, and get it looked at rather than waiting to see if it settles down.

Does it matter whether I am on bottles or natural gas?

It changes where the problem is likely to be and where you should be sniffing. Bottled LPG sits heavier than air and pools at ground level, so the bottles, the regulator and the hoses around them are the first place to check. Reticulated natural gas is lighter than air and rises, so it collects up high and behaves quite differently in an enclosed space.

It is the first thing we ask on the phone, along with where you smell it and what you were doing at the time.

What happens when a gasfitter comes out?

We start with those same questions, then work through the system properly. That normally means a pressure test to see whether the installation is holding, and a bubble test with leak detection fluid on the joints and fittings to find exactly where any loss is coming from. We also look at where the appliance and its flue sit in relation to windows and doors, because that is often the real explanation.

Sometimes the outcome is a repair. Sometimes, as it was on that job in Massey, the outcome is simply an explanation and the reassurance that the appliance is behaving as it should.

Who do I call?

Gas work has to be done by a certifying gasfitter, and anything involving an appliance, a bottle set or a gas line is not a DIY job. If you rent, tell your property manager or landlord as soon as you notice it and let them arrange the visit. If the smell is strong and constant, do not wait for that process. Get out and ring your gas supplier’s emergency line or a gasfitter straight away.

Common questions

Is a short gas smell when the hot water starts always normal?

Not always, but it is the most common explanation by a long way. Continuous flow heaters produce a brief smell at ignition, and it becomes noticeable when the unit is mounted close to a window or a door. The two things that make it normal are timing and duration. If it only happens as hot water starts and clears within seconds, that is ignition. If it lingers, or turns up when no gas is being used, get it checked.

Can I turn the gas off myself while I wait?

If you are on bottles and the valve is outside and easy to reach, turning it off by hand is reasonable. Do not go hunting for it in a confined space, and do not use a torch or your phone light close to the bottles. On natural gas the main tap is usually at the meter, and you should ring the network’s emergency line rather than working on anything yourself. If you are unsure, leave it alone, get outside and make the call.

Why does the smell seem worse in winter or on still days?

Air movement is doing most of the work. On a windy day, ignition smell blows away before anyone notices it. On a still, damp morning it hangs around the wall and finds its way inside. Winter also means more hot water use and more closed windows in the rest of the house, so the bathroom window ends up being the one that is open. The gas has not changed, only the conditions around it.

The bottles smell after they get swapped over. Is that a leak?

A faint smell right at the moment of a bottle change is normal, because a small amount of gas escapes when the connection is broken and remade. It should clear within a minute or two once the fitting is done up. What is not normal is a smell that is still there hours later, or one that keeps coming back near the bottle set. That points at a connection or a fitting rather than the swap itself, and it is worth having looked at.

Does a gas smell mean my hot water unit needs replacing?

Usually not. Most of these calls end with either an explanation about ignition or a repair to a specific fitting, not a new appliance. Continuous flow heaters last a long time when they are serviced, and a smell on its own says nothing about the condition of the unit. If your heater is old and also giving you fluctuating temperatures or fault codes, that is a separate conversation worth having.