Instantaneous or continuous flow gas hot water systems are highly popular these days for their efficiency, space-saving design and sleek look, and – of course – that never-ending hot water supply. But when those instant gas hot water system problems strike, it can be hugely frustrating – especially when you’re not sure whether the fix is easy and obvious, or if it needs a professional.
In our guide, we’ll walk you through some common instant gas hot water system problems and highlight which ones you might be able to fix yourself – safely and legally – and which ones should always be left to a licensed hot water plumber in Brisbane and beyond.
How Does an Instant Gas Hot Water System Work?
Instant gas water heaters warm up water as you need it instead of holding heated water in a storage tank. Cold water travels into the system so a gas burner can heat it as it flows through a coiled copper pipe called a heat exchanger. The heat is applied directly and results in instant hot water.
No heated water needs to be stored at any point like most electric units, and the gas burner only activates when the hot tap is turned on. This means both energy and cost savings.
So there can be different problems for instant gas vs electric storage hot water. Let’s start with the quick wins.
5 Common problems you can fix yourself
Here are some issues that many Brisbane homeowners can check and resolve without needing tools, experience, or a plumbing licence.
1. Check the power supply
If you have an instant gas hot water not working completely, the issue might not be gas-related at all. Instant systems usually also rely on electricity as well for ignition and control. If the power point has been accidentally switched off or the safety switch has tripped, the unit won’t start at all.
DIY Fix:
- Check the outdoor power point (if applicable)
- Reset the switchboard if something has tripped.
2. Reset the unit
Sometimes, your system just needs a basic reset – especially after a power outage or surge. This is one of the simplest instant gas water heater troubleshooting tips of all.
DIY Fix:
- Turn off the unit at the power point
- Wait 30 seconds
- Turn it back on and test the taps
This simple step can sometimes clear minor electronic faults.
3. Check tap flow rates
Modern gas hot water units require a minimum flow rate to trigger the burner. If your shower head or tap restricts flow too much, the system may not fire – or you might find your instantaneous hot water goes cold suddenly.
DIY Fix:
- Try turning the tap on fully to see if the unit engages
- Avoid ultra-low flow shower heads that drop below 3L/min.
4. Is the gas on?
If you’ve recently moved in or had another gas appliance serviced, your gas valve may have been turned off. This could easily explain a gas instant hot water not working properly.
DIY Fix:
- Check that the gas isolation valve beside the unit is in the open (parallel) position
- Make sure your gas meter hasn’t been locked off due to unpaid bills or disconnection
- Are you sure the gas bottle isn’t simply empty?
5. Temperature settings
Finding your gas hot water not hot enough? The issue may be the controller settings rather than the system itself.
DIY Fix:
- If your system has a digital controller, try adjusting it to a higher temperature
- Be cautious not to exceed safe limits (50°C is standard for bathrooms)
- If the temperature isn’t adjusting, the issue might be deeper – more on that below.
Issues that need a licensed professional
Not every problem has a DIY solution. These common faults either require:
- Special tools
- Specialist knowledge
- Or are illegal to fix without a plumbing/gasfitting licence in Queensland.
1. Burner or ignition failure
If your system won’t ignite or you hear clicking but no flame, it could be a blocked burner, faulty ignition module, or sensor issue. This is a common cause of so many instantaneous gas hot water system troubleshooting calls.
Professional Required:
- Internal parts must only be accessed and repaired by a licensed gasfitter
- A qualified plumber can safely test components, replace sensors, and check flame rectification.
2. Brand-specific hot water system issues
Not all hot water problems are universal – some are highly specific to the make and model of the system you have. Different hot water brands use different components, sensors, and control boards, which means the same symptom (like inconsistent heating or flashing error codes) might have a different cause depending on the unit.
For example, Thermann 26 problems may include intermittent ignition or temperature fluctuations tied to flow rate sensors. Rinnai systems, on the other hand, may show error codes related to water pressure or flame failure – while Bosch units occasionally require specific reset procedures or controller reprogramming.
Professional Required:
Troubleshooting these kinds of issues requires brand-specific knowledge, tools, and access to internal diagnostics. These are rarely DIY-friendly fixes, but require a licensed plumber/gasfitter with experience in that specific system.
3. Fluctuating temperatures
If your gas hot water goes hot then cold, the issue could be:
- A faulty tempering valve
- Water flow rate fluctuations
- A dirty water filter
- Or even a partially blocked heat exchanger.
Wondering why does my gas hot water keep going cold in the middle of a shower? It could be any of these – and all require tools and knowledge to test and repair.
Professional Required:
Never attempt to open sealed components or valves yourself. A plumber will:
- Test the valve
- Clean filters
- And ensure proper burner performance.
4. Internal water leaks or error codes
Visible water dripping from the hot water unit or flashing error codes often point to a more serious issue. This might include:
- Blocked flue or vent
- Faulty heat exchanger
- Internal corrosion
- Gas valve failure.
These faults are DANGEROUS if mishandled. Even if you’re confident, it’s not legal to repair them yourself.
Professional Required:
A licensed plumber/gasfitter can assess and repair all internal components safely, in compliance with QLD laws.
5. Poor water pressure or cold patches
If your instantaneous hot water goes cold occasionally, or pressure drops when using multiple taps, your unit might be undersized, or your plumbing layout may need upgrading or servicing. The strainer valve that removes solids near the inlet valve might be blocked and need cleaning or replacement. Mineral buildup can also cause low hot water pressure, this will require flushing your system.
Professional Required:
An expert can:
- Service your hot water unit
- Assess your household usage
- Recommend system upgrades
- Or even relocate the unit for better performance.
Still having trouble? Here’s what to do next
If you’ve tried the basics and your instant gas hot water system problems aren’t resolved, don’t risk damaging your unit – or worse, breaching gas regulations. Here at S&J Plumbing and Gasfitting, we proudly offer expert, fully-licensed support for every complaint – from gas hot water not hot enough to major repairs and full system replacements.
We work with all major brands and can provide fast service across Brisbane, including Brisbane Northside, Brisbane Southside, Logan, Moreton Bay, Redland Bay, and Ipswich.
Call S&J Plumbing And Gasfitting today
From controller resets to full system diagnostics, S&J Plumbing and Gasfitting has your hot water needs covered. We’re licensed, experienced, and local – and we’ll always explain what you can fix yourself and what needs a pro.
Get in touch today for expert help with your instant gas hot water system, and keep the hot water flowing without the stress.