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 into 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 instantaneous gas hot water systems on a daily basis and know all the common problems you might encounter. We’ve even got you covered for some basic troubleshooting to help you identify the problem.

But first, how do instant hot water systems work?

How an Instant Gas Hot Water System Works

Instantaneous gas hot water systems only heat as much water as you need. They take cold water in from a cold inlet pipe, pass it through a copper heat exchanger where it is heated, and then through a hot outlet pipe and to the fixture you want hot water from.

Your water heater’s pilot light is only turned on and heating when it detects that a hot water tap has been turned on. Likewise, it turns off when you turn the hot water tap off!

While you won’t have problems often, there are a few opportunities for error 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 the case that it’s simply set too low, this is an easy fix. Simply adjust the thermostat to be your desired temperature!

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

Alternatively, it could be that your instant hot waters system’s flow rate is not able 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 and don’t use the dishwasher or washing machine at the same time as the shower.

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, as well as 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.

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 water temperature. This type of water heater likely won’t be able to supply enough hot water for four bathroom homes in cold climates.

There’s No Hot Water at All

person turning hot water tap on

The first and most obvious place to start if you’ve got no hot water at all is checking that your instant gas hot water system is plugged in and turned on at the power outlet. 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. This can be fixed with a call to your gas supplier! If they are working, there could potentially be a problem with the gas connection to your water heater which will require the help of a qualified gas-fitter.

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 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. This will need to be addressed by a qualified plumber.

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 which 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.

Here at Metropolitan Plumbing, we work with this type of gas hot water system on a daily basis. No matter what your problem is, 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!


Published: 25 May, 2021

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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:
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Trent was brilliant, arrived on time and did a great job replacing our kitchen mixer tap on a Saturday evening after our existing tap fell apart. Hoping we don’t need emergency services again, but would definitely use them again!

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