person running hot water for a bath

You Need to Know These Instant Gas Hot Water Problems

Instant gas hot water systems, also known as continuous flow gas hot water systems, are a great investment in the running of your home. They’re energy-efficient, cost-effective, compact and better for the environment! But what do you do when they’re not working quite right?

Our hot water experts work with gas instantaneous water heater systems on a daily basis and know all the common problems you might encounter. We’ve even provided some basic troubleshooting to help you identify the problem.

But first, how do instant gas water heaters work?

How an Instant Gas Hot Water System Works

Instantaneous gas hot water systems heat only the required amount of water as you need it. They draw cold water from an inlet pipe, pass it through a copper heat exchanger to heat it, and then channel it through a hot outlet pipe to the desired fixture.

The water heater pilot light activates for heating only upon detecting that a hot water tap is on. Similarly, it shuts the pilot flame off when you turn off the hot tap.

Although problems are rare, a few potential errors can occur in the water heating process.

Common Instant Gas Hot Water Problems and How to Fix Them

We’ve compiled the most common instant gas water heater problems and what you can do to fix them.

Water Is Only Lukewarm

There are a couple of reasons why your instant water heater might only be providing you with lukewarm water.

The first is that your hot water unit thermostat is set too low or is faulty. If it’s simply set too low, all you need to do is adjust the thermostat to a more suitable yet safe temperature.

In the case of a faulty thermostat, you’ll need the help of a professional plumber to repair or replace it.

Instant Gas Hot Water Demand Exceeds Supply

Alternatively, it could be that the flow rate of your instant hot water system is unable to keep up with your home’s hot water demands. There are two ways you can go about solving this issue.

First, you can adjust your family’s hot water use so that not everyone is using it at once. Start by staggering your showers throughout the day rather than all at once. Perhaps avoid using the dishwasher or washing machine at the same time as the shower as well.

Spreading out your hot water use can be a major inconvenience, especially for large families. Instead, it might be worth upgrading to an instant hot water unit with a greater flow rate than your existing one. Or you could also install an additional unit to work in tandem with your existing one!

The right flow rate for your home depends on how much hot water you expect to be using at once. Also important is the general climate of your home. Generally speaking, you can approximate your home’s hot water use with the number of shower outlets in your home.

Climate Conditions

For those living in a warm climate, a flow rate up to 20 litres per minute (L/min) will be enough for one-bathroom homes. One-to-three-bathroom homes will need 20-30 L/min and four-bathroom homes will need greater than 32 L/min.

Those of you living in a colder climate will need greater flow rates to achieve the same hot water pressure and temperature. This type of continuous flow system likely won’t be able to supply enough hot water for four-bathroom homes in cold climates.

person turning hot water tap on

There’s No Hot Water at All

The first thing to check is that you’ve actually plugged in and turned on your instant gas hot water system. If it’s not, then all you need to do is plug it back in and turn it on.

Next on the list to check is your gas connection. Are your other gas appliances in your home working? If not, it’s most likely a problem with your gas supply. You can fix this with a call to your gas supplier! If they are working, there could potentially be a problem with the gas meter. It might also be an issue with the connection to your water heater. Either way, it will require the help of a qualified gas fitter.

But if it’s neither of those? Remember how we said your instant hot water starts heating when it senses a hot water tap has been turned on? If the flow rate from this tap is not high enough, it won’t detect the tap being on and so won’t turn on to heat your water! This can happen when you have low-flow fixtures installed.

This problem can often be solved by running the hot water for a couple of minutes or swapping over to fixtures with a flow rate that your hot water heater can recognise.

Your Water Is Sporadically Hot and Cold

There are a few reasons why your water might be sporadically hot and cold. Your fixtures might have a restrictor on them or are faulty so your water heater struggles to determine whether or not it is a hot water tap. This can cause it to irregularly heat your water.

Alternatively, the gas supply to your hot water unit might not be sufficient, causing it to turn on and off unexpectedly. You will need a qualified plumber to address this problem.

There’s Less Hot Water or a Lower Water Pressure

If your instant hot water system is producing less hot water or you’ve got low pressure water, there are a couple of potential causes for this.

It might be caused by the cold inlet strainer valve being blocked. This can reduce the amount of water or water pressure coming from your instant water heater. This valve filters water being pumped into your water heater so debris and rust can’t enter it. A broken or faulty thermostat can also cause this problem.

Gas Hot Water Experts

Here at Metropolitan Plumbing, we work with this type of gas hot water system on a daily basis. No matter what your problem is, whether it’s with the flow sensor, gas valve meter or another component, we’ll be able to identify and solve it to get your hot water back up in no time.

For an instant gas hot water system expert, call Metropolitan Plumbing and we’ll have someone at your door today!

Please note: This information is provided for advice purposes only. Regulations differ from state to state, so please consult your local authorities or an industry professional before proceeding with any work. See our Terms & Conditions here.


Published: 2021-05-25

Need a Plumber Today?

Electrical, plumbing and air conditioning work is essential and we will be available to do the jobs you require in your home. Our friendly technicians are taking all precautionary measures and keeping to best hygiene practices.

Plumbers You Can Trust

Our Promise to You

Honest Plumbing Services Icon


We believe in transparency. We will guide you through our process, answer your questions and provide you with an upfront, no obligation fixed prices.

Committed to Plumbing Service Excellence Icon


No matter how big or small the job is, whether you're a new or returning customer, we treat every job as important and strive for success.

Professional Expert Plumbers Icon


We know our job site is your home and we completely respect that. We arrive neat and clean, and tidy up after we've completed the job.

zip pay Options
Zip Pay Payment Options Image

Now Available!

Plumbing finance options** with trusted pay later options

What Our Happy Customers Have to Say

This is why we do, what we do!

Metropolitan Plumbing are proud winners of 2021 and 2020 Product Review awards in the plumbing category. These awards highlight our dedication to outstanding customer service. Product Review provides a platform for real-life experiences. Check out some of our customers' reviews below:
5 stars rating

Dave.C was very friendly and professional especially for a Sunday. He was able to identify the cause of the leaky shower head, and provide two quotes. He was also able to show what the issue was and was able to advise what he had done to fix it. Thank you.

Tyrell Tongz - QLD
5 stars rating

They replaced our old, malfunctioning toilet. The installation was quick, and they checked for any leaks thoroughly. Reliable service we can count on!

Anna Cunning - QLD
5 stars rating

I had a toilet that wouldn’t stop running, and it was wasting so much water. They arrived promptly, diagnosed the issue, and replaced the faulty parts. Now my toilet works perfectly. Great service and reasonable rates.

Caity Waters - QLD
  • Wilson Hot Water Logo

    Wilson is an Australian owned and operated hot water system supplier with products to suit any need. Rest assured our technicians can install and service your Wilson hot water system.

  • Vulcan Hot Water Logo

    Vulcan hot water systems are forged tough so that they can handle Australia's changeable climate without missing a beat.

  • Thermann Hot Water Logo

    Thermann is one of the most efficient water heating systems around, with a range of options from solar boosted to heat pumps. We can install, service and repair your Thermann system.

  • Saxon Hot Water Logo

    Unfortunately, Saxon no longer produces heating units, but Metropolitan can still service, repair or replace your old Saxon system.

  • Stiebel Eltron Hot Water Logo

    Stiebel Eltron was established in Germany, 1924. With over 95 years of experience in making hot water units, you can expect quality.

  • Rinnai Hot Water Logo

    Rinnai is one of the biggest names in hot water systems. Metropolitan Plumbing has worked with Rinnai hot water systems for more than 25 years.

  • Rheem Hot Water Logo

    Rheem has been going steady, hot and strong since 1939 with a comprehensive range of solar, heat pump and gas hot water solutions.

  • Everhot Hot Water Logo

    No matter how big or small your requirements are, Everhot has the right system. We at Metropolitan can help install or service your Everhot system.

  • Edwards Hot Water Logo

    Edwards is recognised for its superior performance and outstanding range of ground and roof mounted units offered in a range of colours.

  • Dux Hot Water Logo

    Dux is the big name in residential and commercial solar, heat pump and gas water heating. We can service and repair your Dux hot water system.

  • Chromagen Hot Water Logo

    Chromagen is an internationally recognised manufacturer of highly efficient hot water systems.  Metropolitan can service, replace or repair your Chromagen system.

  • Bosch Hot Water Logo

    Bosch provides quality hot water to thousands of Australians with its wide range of solar, gas and electric units.

  • AquaMAX Hot Water Logo

    AquaMax is the household name in hot water. We can take care of all of your Aqua Max needs from installation to repair.

Metropolitan Plumbing - Product Review img Metropolitan Plumbing - Product Review img