Instant gas hot water error codes: what they mean and fixes

We know losing hot water is frustrating, especially when a digital display shows a blinking number and you need help now. In this guide we explain common hot water alarm numbers such as 11, 12 and 13, what they often point to and the quick checks you can safely do at home.

First, confirm the gas supply is open at the meter or LPG bottles and check electrical power. Many Rheem and other tankless units halt until power and ignition reset. A simple power-off, wait, then power-on often clears temporary faults.

Some faults need a licensed technician. Examples include blocked condensate neutralisers, combustion path obstructions and thermistor faults. We provide plain-English troubleshooting and a conservative stop‑and‑call approach to protect your heater and home.

For 24/7 Melbourne response, call OnCall Emergency Plumbers on 1800 571 216. We handle tankless systems, blocked drains, burst pipes and leak repairs with quality parts and experienced technicians.

Key Takeaways

Check the gas supply and power first; many displays reset after a restart.
Codes like 11–13 often point to supply, combustion or ignition faults.
Leave condensate, combustion path and thermistor faults to licensed technicians.
Hard water and cold snaps increase scale and ignition issues.
We offer 24/7 Melbourne service — call 1800 571 216 for urgent assistance.

Why your hot water shows error codes and how we approach safe troubleshooting in Australia

When a controller flashes and hot water stops, the fault usually stems from supply, ventilation or electrical issues. We prioritise safety and sensible checks before any hands‑on work.

Safety first: treat any smell of gas as an immediate stop and call a licensed professional. Never open or disassemble a gas appliance yourself.

Gas, electricity and ventilation basics

Tankless units rely on both gas and power to operate. If electricity is out, electronic ignition and controls won’t run and no hot water will be produced.

Confirm the supply at the gas meter or LPG valve and check the electrical feed before further checks. Restricted air intake or blocked exhaust can trigger automatic shutdowns or high temperature readings.

Melbourne conditions to consider

Cold snaps lower inlet water temperature and can expose marginal pressure or combustion issues. Hard local water also leads to scale in the heat exchanger, which reduces heat transfer and can create intermittent temperature faults.

We perform only low‑risk checks first: verify gas valve position, clear external vents and confirm power.
Any work involving burners, valves or flues is handled by licensed trades for safety and compliance.
If safe checks don’t restore operation, our Melbourne team can attend 24/7 to diagnose and repair with reputable parts.

For urgent assistance call 1800 571 216 — we provide fast, affordable service and use quality materials to protect your home’s comfort.

Quick checks before you dive into fixes

Before diving into repairs, run a few fast checks to rule out common supply and power issues. These steps are safe, take little time and often restore hot water without tools.

Confirm the gas supply at the gas meter or LPG cylinders is fully on

Check the isolation valve at the gas meter or the LPG cylinder valve is fully open. Partially closed valves can starve the burner and cause ignition problems.

Verify electrical power to the unit and controller after any outage

Ensure household power is present and the outdoor unit and controller are powered. After outages you may need to reset breakers or RCDs before the unit will restart.

Look for flashing indicators on the controller and note the exact error code

Observe the controller display and write down the exact code and any flashing pattern. Photographing the screen and surrounding area helps our team diagnose the fault faster.

Safe reset: follow instructions to power the unit off, wait a few minutes, then power on and open a hot tap — many transient lockouts clear this way.
Check inlet and outlet isolation valves are open to maintain correct water flow through the heater.
Scan around the appliance for leaves, lint or debris at air intake and exhaust; clear them without removing covers.
If you smell gas, see burn marks, or hear arcing, stop and call our licensed team immediately — do not continue troubleshooting.
Avoid repeatedly cycling the appliance; allow time between attempts so internal protections can reset.

Check	Why it matters	What to do
Gas meter valve	Partial closure reduces fuel supply	Open fully and re-test unit
Electrical supply	No power = no ignition or controller function	Reset breakers/RCDs, then restart unit
Controller display	Shows code or flashing pattern for diagnosis	Note or photograph the code for technicians
Air intake/exhaust	Blockages cause combustion faults	Clear debris around vents without opening covers

If these quick checks don’t clear the issue, we can help 24/7 in Melbourne with fast, affordable service using quality materials. Call 1800 571 216.

instant gas error codes decoded: common meanings and fast fixes

A flashing display often points to a simple supply, airflow or sensor issue. We outline common numeric faults and practical steps you can try safely.

Error 11 — no ignition or no gas supply

Confirm the gas meter and any appliance isolation valve are fully open. Ensure the unit has power, then perform a safe restart and test a hot tap.

Errors 12 & 13 — insufficient supply and poor combustion

Check vents for wind‑borne debris and inspect inlet and exhaust terminations. Restricted air or low supply pressure causes poor combustion and cutouts.

Error 05, P1 and 29 — vents, flow and condensate

Error 05 flags blocked air paths; remove leaves or nests from grills. P1 means low water flow — clean the inlet strainer and open isolation valves. Error 29 needs a licensed technician for condensate neutraliser service.

Thermistor faults, 31–34, and controller issues 65/76

Sensor faults need professional testing; do not open the casing. Controller or volume faults may require wiring checks and recalibration by a licensed technician.

Quick rule: power off, wait, power on; if a code persists, avoid repeated ignition attempts.
We can attend 24/7 across Melbourne with licensed technicians and quality parts — call 1800 571 216.

Code	Likely cause	Action
11	No ignition / valve closed	Open valve, restart unit
12 / 13	Low supply / poor combustion	Check vents, call tech if pressure low
P1	Low water flow	Clean inlet strainer, increase flow
29	Condensate neutraliser blocked	Stop use, book licensed service

Rheem hot water specific codes and what they point to

We explain the common Rheem signals and what they usually mean for your heater. The guidance helps you run safe checks and know when to stop and call our team.

Rheem 1L — limescale in the heat exchanger

Code 1L points to scale building on the heat exchanger surfaces. Scale cuts heat transfer and causes unstable outlet temperature.

What to do: professional descaling is recommended. We can assess severity and restore proper temperature performance.

Rheem 11 — gas shutoff not fully open

This often clears when the valve is fully opened and the unit is reset. If the message returns, a supply or ignition component may need service.

Rheem 12 / 13 — fuel supply and combustion quality

These indicate poor combustion or low supply pressure. Check air intake and exhaust for blockages and ensure no wind shields obstruct vents.

If pressure or flame stability is suspect, a licensed technician must test the supply and make repairs.

Reset procedure: when it helps and when it doesn’t

Turn the heater and controller off, wait about 20 minutes, then power up and open a hot tap to restart ignition. This fixes many transient faults.

If a code persists, do not repeatedly cycle the unit. Persistent sensor, control or drain faults need professional diagnostics.

P1 — low flow: clean inlet filter and open isolation valves.
05 — air/exhaust path: inspect visible vents; don’t remove sealed covers.
29, 31–34, 65, 76 — condensate, thermistor and control faults need licensed attention.

Rheem message	Likely cause	Action
1L	Limescale on heat exchanger	Book professional descaling
11	Shutoff valve partly closed	Open valve, reset unit; call if it returns
12 / 13	Low supply / poor combustion	Clear air paths, have supply pressure checked
P1 / 05	Low flow / blocked vents	Clean filters, clear external vents

We diagnose and repair Rheem hot water systems across Melbourne 24/7. Our experienced team uses quality materials and provides affordable, emergency-focused service. Call 1800 571 216.

Step-by-step troubleshooting you can try safely at home

A step‑by‑step approach helps you rule out simple supply and flow problems fast. Follow these low‑risk checks in order and stop if you smell anything unusual or see damage. If the unit still won’t operate, photograph the display and contact us.

Restart sequence

Close all hot taps, switch the heater and controller off, then wait five minutes. This pause lets internal protections reset.

Switch the unit and controller back on, then open a hot tap to re‑trigger ignition. Many faults clear with this simple restart.

Ventilation and air path

Inspect air intake grills and exhaust terminations for leaves, lint or debris. Remove loose material without taking covers off the appliance.

Avoid blocking vents around the cabinet; good air supply is essential for safe combustion and correct operation.

Water flow and pressure

Gently clean the cold inlet screen filter and ensure inlet isolation valves are fully open. Poor water flow can stop the burner from firing.

Stabilise flow by opening the hot tap further; some units require a minimum water flow and pressure to heat properly.

After outages

Electronic ignition units cannot heat without mains power. After an outage, restore power, perform the restart sequence and allow the controller time to reinitialise.

Do not adjust internal gas components, pressure settings or control wiring—these need licensed testing.
If messages persist after following these instructions, take a photo of the display and call us for compliant diagnostics.
Our Melbourne team is available 24/7 for affordable emergency service using quality parts. Call 1800 571 216.

Check	Why it matters	Action
Restart	Clears transient lockouts	Power off 5 minutes, power on, open hot tap
Air path	Blockages cause combustion faults	Clear grills; do not remove sealed covers
Inlet filter	Low flow prevents burner activation	Clean screen; open isolation valves fully

Beyond the code: issues that often cause recurring faults

Recurring faults often have hidden causes that simple resets won’t fix. We find the same patterns in many Melbourne homes and businesses. Left unchecked, these issues repeat each season and shorten component life.

Mineral buildup and temperature instability

Limescale inside the heat exchanger reduces heat transfer. That forces longer burner cycles and can trigger protective shutdowns or a temperature fluctuation.

Reduced flow from scale or debris at the inlet also raises outlet temperature quickly. Regular descaling and inlet cleaning prevent these recurring problems.

Combustion, flues and failing components

Combustion quality relies on clear air paths and correct flue termination. Obstructions, poor venting or an ageing fan destabilise flame and trip sensors even when the burner lights.

Supply variability — whether water, gas or electrical brownouts — and system overloads also cause repeated trips. We check sensor accuracy, fan operation and pipe sizing to find the root problem.

Limescale in the exchanger causes temperature faults and reduced efficiency.
Blocked vents or weak fan affect combustion and sensor readings.
Supply swings — gas or water pressure and electrical dips — create sporadic faults.

Cause	Effect	Action
Limescale in exchanger	Temperature instability	Professional descaling
Blocked flue / poor air	Combustion faults	Clear vents, test fan
Supply or sensor drift	Sporadic shutdowns	Verify supply, replace sensor

For recurring problems in Melbourne, we provide comprehensive, affordable service 24/7 using quality materials from reputable brands. Call 1800 571 216 and we’ll diagnose and fix the root cause of your hot water system.

Need it fixed now? Call OnCall Emergency Plumbers — Melbourne’s 24/7 instant hot water specialists

When hot water fails at the worst moment, a prompt, professional response restores comfort and safety. We’re Melbourne‑based, available 24/7 and focused on fast, safe repairs for tankless and storage systems.

Licensed, experienced and affordable emergency repairs on gas hot water systems

We are licensed plumbers who diagnose display messages, test supply and restore operation. After power interruptions many Rheem and other tankless units show faults; we reset, test and repair to get reliable hot water back quickly.

We use quality materials from reputable brands to ensure lasting results

Our team fits manufacturer‑approved parts and follows compliance standards. This reduces repeat visits and protects warranties.

Fast response across Melbourne — call 1800 571 216

We provide 24/7 emergency service across Melbourne with rapid dispatch and clear pricing. Our plumbers carry common parts to complete most repairs on the first visit.

We diagnose supply, venting, ignition and flow related faults safely and efficiently.
We handle general plumbing, blocked drains, burst pipes and leak repairs alongside hot water work.
Experienced professionals who prioritise safety, affordability and clear communication.

Service	What we do	Benefit
24/7 emergency service	Rapid attendance across Melbourne	Minimal downtime for your household
Diagnostics	Inspect supply, vents and sensors	Correct root cause fixes
Repairs & parts	Manufacturer‑approved materials	Long‑term reliability

Book now for immediate service — call OnCall Emergency Plumbers on 1800 571 216.

Conclusion

To wrap up, note the displayed code and try the timed reset, then record how the unit behaves. These simple troubleshooting steps often solve supply or flow issues and speed professional diagnosis.

Persistent error messages such as 11, 12, 13, 05, P1, 29, 31–34, 65 or 76 commonly relate to gas supply, combustion air, water flow, thermistors or condensate systems. Power outages can halt electronic ignition and need a proper restart.

If a code remains, avoid repeated restarts and call our licensed team for compliant testing and repair. For fast, affordable help anywhere in Melbourne — any time — call OnCall Emergency Plumbers on 1800 571 216.

We use quality materials from reputable brands and provide 24/7 emergency service to restore your hot water system reliably.

FAQ

Why does my instant gas hot water system show an error code and how do we safely start troubleshooting in Australia?

Error indicators can come from gas supply interruptions, electrical faults, sensors, poor ventilation or water flow problems. We first isolate safety risks: turn off electrical power at the switchboard, close the gas isolation valve if safe to do so and ensure the area is well ventilated. Never attempt internal repairs on gas valves or combustion components — call a licensed technician for those tasks.

What basic safety checks should we perform for gas, electricity and ventilation on tankless units?

Confirm the gas meter or LPG cylinders are open and the service pipe pressure is normal. Verify mains power or the RCD hasn’t tripped and the controller has power. Check air intake and exhaust flues for obvious blockages or bird nests. If you smell gas, evacuate, isolate supply at the meter if trained, and contact emergency services.

Are there Melbourne‑specific conditions that affect hot water systems?

Yes. Cold snaps can increase demand and reduce flow temperatures, power outages interrupt electronic ignition, and local water quality or low pressure can lead to mineral build‑up or flow faults. We factor these when diagnosing repeat faults in Melbourne properties.

What quick checks should we do before attempting fixes?

Confirm the gas supply at the meter or LPG is fully on, verify electrical power at the unit and controller after outages, and note any flashing lights or exact message on the controller. Take photos of the display; they help technicians diagnose the fault remotely.

What does Error 11 mean and what can we check quickly?

Error 11 usually indicates no ignition or interrupted gas supply. Check the main gas meter, isolation valves and any external shutoffs. Follow the unit’s relight sequence if it’s safe; if the unit still fails to ignite, stop and call a licensed gas fitter.

What do Error 12 and 13 point to and how do we test for combustion issues?

Errors 12 and 13 relate to insufficient gas supply or poor combustion. Inspect the air intake and exhaust for blockages, ensure vents are clear, and confirm gas pressure is adequate. Combustion issues often need a qualified technician to test gas pressure and burner condition.

How should we respond to Error 05 about air supply or exhaust vent blockage?

Turn off the unit, visually inspect intake and exhaust outlets for obstructions, remove debris or nests, and verify the flue termination is installed correctly. If the blockage sits inside the flue system, engage a licensed service technician to clear it.

What is Error P1 and how can we improve low water flow?

Error P1 signals low water flow. First, check that inlet isolation valves are fully open and clean the inlet filter screen. Increase the tap flow rate to confirm the unit detects adequate flow. Persistent low flow may indicate plumbing restrictions or a faulty flow sensor.

What does Error 29 mean — is it something we can fix ourselves?

Error 29 often shows a condensate neutraliser or drain blockage. This requires a licensed technician to inspect and replace the neutraliser or clear condensate traps. Avoid pouring chemicals down the condensate line; that can damage components and void warranties.

What do thermistor errors (31–34) indicate and what should we check?

Thermistor faults relate to temperature sensors — inlet, outlet, heat exchanger or ambient. We check wiring connections, visible damage and any loose plugs at the controller. If wiring and plugs look sound, the sensor or control board may need replacement by a licensed technician.

What do Error 65 and 76 mean regarding water volume control and controller communication?

Error 65 often relates to water volume control issues; Error 76 points to remote or controller communication faults. Check remote controller batteries, wiring and connectors for corrosion or looseness. If the controller shows no response after resets, arrange professional service to test the control board and communication harness.

What are common Rheem hot water codes and their likely causes?

Rheem codes often map to similar faults: 1L suggests limescale in the heat exchanger and may need descaling; 11 indicates the gas supply or gas shutoff isn’t fully open; 12/13 point to fuel supply or combustion problems. Follow Rheem’s reset procedure first, but persistent faults require an authorised Rheem technician.

When does a simple reset help and how do we perform it?

A reset can clear transient faults after outages. Power down the unit at the isolating switch, wait at least five minutes, power up and reopen hot taps. If the same code returns, do not repeat resets indefinitely — document the code and contact service support.

What safe step‑by‑step troubleshooting can we try at home?

Close hot taps, switch the unit off, wait five minutes, power it back on and open a hot tap to trigger ignition. Check intake and exhaust for blockages, clean inlet screens, and ensure inlet and outlet isolation valves are open. Never access internal combustion components or attempt gas valve repairs yourself.

Why won’t electronic ignition units heat after a power outage?

Electronic ignition systems require mains power for the control board and fan. After an outage the unit will not light until power returns and the control completes its start sequence. Ensure RCDs and power isolators are reset before further diagnosis.

What recurring issues often lie beyond the displayed code?

Mineral scale build‑up in heat exchangers reduces heat transfer and triggers temperature faults. Combustion and flue issues can cause unstable flames and sensor faults. Recurrent faults may indicate maintenance needs such as descaling, flue cleaning or burner servicing by a licensed technician.

How quickly can we get emergency repairs in Melbourne from OnCall Emergency Plumbers?

We offer 24/7 emergency repairs across Melbourne. Our licensed technicians carry quality parts from reputable brands and aim for a fast response. For urgent service call 1800 571 216 — we triage faults remotely where possible and dispatch appropriate crews.