In this guide

  1. Before anything else: three quick checks
  2. Diagnose by system type (electric, gas, continuous flow)
  3. Rheem error code reference table
  4. What you can safely DIY vs what needs a plumber
  5. Stop immediately: signs of serious fault
  6. Rheem maintenance schedule to prevent future failures
  7. FAQs

Cold water when you expected hot is one of those problems that goes from inconvenient to genuinely disruptive within minutes. The good news: most Rheem hot water faults follow a predictable pattern, and the majority can be diagnosed quickly with a few targeted checks before you pick up the phone.

SPS Plumbers has been servicing, repairing, and replacing Rheem systems across Sydney for over 20 years. This guide is built from that real-world experience, not a generic troubleshooting list. We've structured it by system type because the diagnostic path for an electric storage tank is completely different from a Rheem continuous flow unit, and conflating the two wastes your time.

Safety first: If you smell gas at any point during these checks, do not attempt any further diagnosis. Leave the property, keep doors open as you exit, and call your gas provider's emergency line or SPS on (02) 9072 0760 immediately. Do not turn any switches on or off.

Before Anything Else: Three Quick Checks

Before diving into system-specific checks, run through these three quick questions. They resolve a surprising number of service calls before any tools are needed.

  • 1
    Is it only one tap, or every hot tap in the house?

    If just one tap has no hot water, the problem is almost always a faulty mixer cartridge or aerator blockage at that fixture — not the hot water system itself. If every hot tap in the house is affected, the fault is at the unit level. This single check tells you where to look first.

  • 2
    Is there any power or gas reaching the unit?

    Check your switchboard for a tripped circuit breaker labelled "Hot Water". For gas systems, confirm your gas meter is on and test another gas appliance (stove, heater). If other gas appliances aren't working either, the fault is with your gas supply, not the Rheem unit.

  • 3
    Is the Rheem unit displaying anything?

    Modern Rheem continuous flow units have a digital display. If it's blank, you have a power issue. If it's showing a flashing light or a numbered code, jump to the error code table below. Older storage tank models without displays — check the relief valve and listen for sounds from the unit.

Diagnose by System Type

Rheem manufactures three broad categories of residential hot water systems. Select yours below for the relevant diagnostic path.

Electric Storage
Gas Storage
Continuous Flow

Rheem Electric Storage System — Diagnostic Steps

Common Rheem electric models: Stellar 160–400L, Optima 50–400L, Heritage 25–400L

  • 1
    Check the circuit breaker and isolator switch

    Go to your switchboard. Find the circuit breaker or fuse labelled "Hot Water" or "HWS". If it has tripped to the middle position, switch it fully off then firmly to on. Also check the waterproof isolator switch on the wall near the tank itself — it should be in the on position. If the breaker trips again immediately after resetting, stop: there is a wiring or element fault that needs a licensed electrician or plumber.

  • 2
    Press the safety reset button

    Remove the access panel on the side of the tank (usually secured with two screws). Behind it you'll find the thermostat. There is a red or black reset button — press it firmly until you feel it click. Replace the panel, restore power, and allow 1–2 hours for the tank to reheat before testing. If the reset button won't stay in, the high-limit thermostat has failed and needs replacing by a licensed plumber.

  • 3
    Check the thermostat temperature setting

    The thermostat dial is also behind the access panel. It should be set to 60°C (the NSW recommended minimum to prevent Legionella growth in storage tanks). If it's been turned down too low, the water will feel lukewarm rather than hot. Adjust to 60°C, replace the panel, and wait 1–2 hours.

  • 4
    Listen for signs of life from the element

    With power restored, place your hand on the side of the tank after 15 minutes. A functioning heating element will generate warmth you can feel through the tank wall. No warmth at all after 20+ minutes suggests a failed heating element. Testing and replacing the element requires isolation of power and is a licensed plumber or electrician job.

  • 5
    Check the TPR valve for continuous dripping

    The Temperature and Pressure Relief valve is on the side of the tank with a pipe running to a drain point. It should not be dripping continuously. Constant dripping indicates either excessive system pressure (common if your property has high water pressure) or a failing valve. In NSW, a continuously dripping TPR valve must be repaired by a licensed plumber — it is a safety issue, not a cosmetic one.

Rheem Gas Storage System — Diagnostic Steps

Common Rheem gas storage models: Stellar 135–360L, Marathon 170–360L, Vitreous 135–170L

  • 1
    Confirm gas supply to the unit

    Check that your gas meter valve is in the open position (handle parallel to the pipe = open). Then test another gas appliance in the home. If the stove or heater also has no gas, the issue is with your gas supply — call your gas provider, not a plumber. If other appliances work fine, the issue is specific to the hot water unit.

  • 2
    Relight the pilot light

    Open the lower access panel on the front of the unit. Locate the pilot assembly — it's the small tube near the burner. Relighting instructions are printed on the label inside the panel of every Rheem unit. The general process: set the control to "Pilot", depress the knob fully while pressing the igniter button repeatedly. Hold the knob depressed for 30–60 seconds after the pilot lights (this heats the thermocouple). Release slowly — if the pilot stays lit, you're done. If it goes out repeatedly, move to step 3.

  • 3
    Suspect a faulty thermocouple

    If the pilot lights but won't stay lit when you release the knob, the thermocouple is almost certainly the issue. The thermocouple is a safety sensor that detects the pilot flame and keeps the gas valve open. When it fails, the gas valve shuts off as a safety measure. Thermocouple replacement is a licensed gas plumber job — do not attempt to bypass it.

  • 4
    Check for sediment buildup symptoms

    If you're getting hot water but it runs out faster than usual, or you hear popping and rumbling sounds from the base of the tank, sediment has built up on the tank floor. This insulates the burner from the water, reduces efficiency, and accelerates tank corrosion. Flushing the tank can help if caught early, but in a tank over 8 years old with heavy sediment buildup, replacement is often the more cost-effective option.

Rheem Continuous Flow System — Diagnostic Steps

Common Rheem continuous flow models: 12L, 16L, 20L, 27L — indoor and outdoor variants

  • 1
    Check both power and gas simultaneously

    Continuous flow units use electricity to power the ignition and control board, and gas to heat the water. Both must be working. Check the circuit breaker at the switchboard AND confirm gas supply to the unit. A unit with power but no gas will display an ignition fault. A unit without power won't display anything at all.

  • 2
    Read the display — note any error codes

    Rheem continuous flow units will display a numbered error code when a fault occurs. Note the number exactly and cross-reference with the error code table below. Do not reset the unit before noting the code — the code tells you (and us) what specifically failed.

  • 3
    Clean the cold water inlet filter

    The cold water inlet filter is located behind a small cap on the water inlet fitting at the base of the unit. Shut the cold water isolation valve (on the pipe feeding the unit), remove the cap, pull out the mesh filter, and rinse it under running water. A blocked filter restricts flow below the unit's minimum activation threshold, meaning the burner never fires and you get cold water only. This is one of the most common and easily fixed issues on Rheem continuous flow units.

  • 4
    Try a unit reset

    If the unit has an error code that doesn't relate to a component failure (e.g. a transient ignition fault), a reset may clear it. The reset button location varies by model — consult your Rheem manual or the label on the unit's front panel. Press and hold per the instructions, then wait 2–3 minutes before testing. If the same error code reappears within one use, the underlying fault is real and needs a plumber.

  • 5
    Check for fluctuating temperature

    If the water temperature is inconsistent — hot then cold then hot — the most common causes are: insufficient gas pressure to the unit, a partially blocked inlet filter affecting the flow sensor, or a failing temperature sensor. These all require a licensed gas plumber to diagnose properly. Do not increase the gas pressure yourself.

Rheem Error Code Reference Table

The following codes apply primarily to Rheem continuous flow (tankless) units. Storage tank models do not typically have digital displays — their faults present through the symptoms described in the diagnostic section above.

Note: Error code behaviour can vary slightly between Rheem model generations. If your code isn't listed here or the description doesn't match what your unit is doing, call us on (02) 9072 0760 and we'll help you identify it.

Error Code What It Means Severity Recommended Action
00 Normal operation / standby Normal No action required
11 Ignition failure — gas not lighting within 8 seconds of activation Moderate Check gas supply, check inlet filter, attempt a reset once. If it persists, call a gas plumber
12 Flame failure — gas ignited then extinguished mid-operation Moderate Often a gas pressure issue or a faulty flame rod. Do not repeat resets — book a service
14 Overheat safety fault — unit exceeded maximum temperature limit Urgent Shut off the unit. Do not reset repeatedly. Call a licensed plumber same day
16 Outlet water temperature too high — measured at heat exchanger outlet Urgent May indicate a blocked heat exchanger or failed temperature sensor. Needs a plumber
31 Inlet thermistor (temperature sensor) fault Moderate Sensor replacement. Licensed plumber job — not DIY
32 Outlet thermistor (temperature sensor) fault Moderate Sensor replacement. Licensed plumber job — not DIY
33 Combustion air or exhaust gas thermistor fault Moderate May indicate a blockage in the flue or a failed sensor. Plumber required
51 Gas valve fault — valve not responding to control signals Urgent Gas component fault. Stop using the unit and call a licensed gas plumber
61 Fan motor fault — combustion air fan not operating within spec Moderate Fan replacement. Licensed plumber job
65 Water flow sensor fault — unit cannot detect flow rate accurately Moderate First clean the inlet filter. If code persists, flow sensor needs replacing
66 Bypass valve fault (temperature control valve not operating) Moderate Component replacement. Licensed plumber job
70 Control board fault — internal circuit error Urgent May require PCB replacement. Call SPS — we carry Rheem components in our service vehicles
76 Communication fault between display and main board Moderate Attempt a full power reset (isolate for 30 seconds). If it persists, call a plumber
90 Combustion fault — incorrect air/gas mixture detected Urgent Do not use the unit. Ventilate the area and call a licensed gas plumber immediately

What You Can Safely DIY vs What Needs a Plumber

Being clear about this is important. Gas and high-voltage electrical work on hot water systems must be carried out by a licensed tradesperson in NSW. Attempting these yourself risks serious injury, voids your Rheem warranty, and can void your home insurance.

Safe to do yourself
  • Reset a tripped circuit breaker at the switchboard
  • Press the safety reset button on an electric unit (once)
  • Adjust the thermostat temperature setting (electric units only)
  • Clean the cold water inlet filter on a continuous flow unit
  • Note and look up an error code on the display
  • Relighting the pilot light on a gas storage unit (following the label instructions exactly)
  • Checking whether the gas meter valve is open
  • Testing another appliance to confirm whether gas supply is at fault
  • Flushing the tank (annual maintenance, following Rheem's documented procedure)
Always call a licensed plumber
  • Any gas line work, gas valve adjustment, or burner repair
  • Replacing the thermocouple on a gas storage unit
  • Replacing a heating element (electric storage)
  • Any repair following an error code 14, 16, 51, 70, or 90
  • Repairing or replacing the TPR valve
  • Replacing thermistors, flow sensors, or PCBs on continuous flow units
  • Anything involving the flue or combustion air path
  • Any work if you can smell gas at any point
  • Any fault that recurs after a reset
  • Installation of a replacement unit

Stop Immediately: Signs of Serious Fault

These symptoms mean you should shut the unit off, leave the area if gas is involved, and call a licensed plumber straight away. Do not attempt further DIY.

  • Gas smell at or near the unit. This is an emergency. Do not operate any switches. Leave the property with doors open, then call your gas provider and SPS.
  • Burning smell or smoke from the unit. Isolate the unit at the switchboard and call a plumber immediately. Do not reset.
  • Water pooling or actively spraying from the unit body. Shut the cold water isolation valve to the unit and call us. A burst tank that's left running can cause significant water damage.
  • Rust-coloured water from hot taps. The tank interior has corroded. This is a health hazard and the tank needs replacing, not servicing.
  • Error codes 14, 16, 51, 70, or 90. These indicate faults that pose a safety risk. Do not repeatedly reset — call a plumber.
  • The unit is more than 12 years old and showing multiple symptoms. At this age, a repair is often a short-term fix. We'll give you an honest assessment of whether repair or replacement makes better financial sense.

SPS same-day guarantee: Call before 10:30am and we guarantee same-day attendance for urgent hot water repairs across Sydney. We carry Rheem parts in our service vehicles and can resolve most faults in a single visit.

Rheem still not working after these checks?

We've been servicing Rheem systems across Sydney for 20+ years. Same-day service, upfront pricing, and a lifetime guarantee on all workmanship. No call-out fee for booked jobs.

Call (02) 9072 0760 Book Online

Rheem Maintenance Schedule to Prevent Future Failures

Most Rheem failures we attend to in Sydney are preventable. The system gives warning signs well before it fails entirely — the problem is that homeowners rarely see them because the unit is tucked away in a cupboard or on an outside wall that nobody checks. A basic annual inspection takes 15 minutes and can add years to a system's life.

Every 6 months
Test the TPR valve

Lift the lever briefly to allow water to flow through the drain pipe. It should flow freely then seal cleanly when you release. Sticky, blocked, or dripping valves need replacing. This test also prevents the valve from seizing in place, which makes replacement harder later.

Every 12 months
Flush the storage tank (storage units)

Attach a hose to the drain valve at the base of the tank, open it, and let sediment-laden water drain until it runs clear. This removes mineral buildup that insulates the heating element (electric) or burner (gas) and reduces efficiency. Skip this for more than two years and you're significantly shortening tank life.

Every 12 months
Clean the continuous flow inlet filter

Remove and rinse the mesh filter on the cold water inlet of your continuous flow unit. Takes five minutes. A blocked filter causes the single most common preventable fault on Rheem instantaneous systems: the unit won't fire because flow is below the activation threshold.

Every 2–5 years
Check or replace the anode rod (storage units)

The sacrificial anode rod inside the tank attracts corrosion so the tank lining doesn't corrode. Once the anode is depleted, the tank itself starts to corrode rapidly. Rheem recommends checking the anode every 2–3 years in areas with aggressive water, and every 5 years in areas with softer water. Sydney's water is relatively soft but anode checks remain worthwhile for tanks over 5 years old.

Every 2–3 years
Full service by a licensed gas plumber (gas units)

A proper gas hot water service includes: burner inspection and cleaning, flue integrity check, gas pressure test at the unit, thermocouple test, thermostat calibration, and an overall safety check. This is the only way to catch component degradation before it becomes a failure. SPS carries out full Rheem services across Sydney — call us to book.

At 8 years
Check the age sticker and plan ahead

Every Rheem unit has a date sticker (on the top of the tank for electric, inside the front panel for gas). Once your system hits 8 years, start planning for replacement — not because it's about to fail, but because when it does fail it'll be at the worst possible time. A planned replacement on your terms is always cheaper and less disruptive than an emergency same-day callout. A 12-year-old unit running fine is still a unit that's likely within 2–3 years of end of life.

Frequently Asked Questions

Why does my Rheem produce hot water for 5 minutes then go cold?
On storage tank systems, this usually means the tank has a failed lower heating element — only the upper element is working, so you're exhausting the small pocket of hot water at the top of the tank quickly. On continuous flow systems, it typically points to a flow rate issue: the unit fires for a moment then loses its flow reading (due to a blocked filter or fluctuating pressure) and shuts down as a safety measure. Both scenarios need a licensed plumber to confirm and fix.
How do I reset my Rheem hot water system?
For electric storage units: isolate power at the switchboard, wait 30 seconds, restore power, then press the red or black reset button behind the access panel on the side of the tank. For continuous flow units: look for a reset button on the front panel or follow the procedure in your Rheem manual (it varies slightly by model — usually press and hold for 3–5 seconds). Always note any displayed error code before resetting. If the fault returns after one reset, the underlying issue needs a plumber — repeated resets on some faults can cause further damage.
My Rheem pilot light won't stay lit — what's causing it?
Almost always the thermocouple. The thermocouple is a safety device that sits in the pilot flame and generates a small electrical signal that keeps the gas valve open. When the thermocouple is cold (or faulty), the gas valve closes as a safety measure — that's why the pilot goes out when you release the button. A new thermocouple is a relatively inexpensive part, but it's a gas fitting job and must be done by a licensed gas plumber. Don't try to bypass or extend it.
How long should a Rheem hot water system last?
A Rheem storage tank (gas or electric) typically lasts 8–12 years. Well-maintained units in areas with good water quality can occasionally reach 15 years, but this is the exception. Rheem continuous flow units generally last longer: 15–20 years with proper maintenance. The biggest life-extender for storage tanks is annual flushing and timely anode rod replacement. The biggest killer is letting sediment build up for years until the element or burner effectively cooks in a layer of scale.
Is it worth repairing my Rheem or should I replace it?
The honest answer depends on the age of the unit and the fault. For a unit under 8 years old with a single failed component (thermocouple, element, thermistor), repair is almost always worth it. For a unit over 10–12 years old, a repair may buy you 1–2 years before something else fails — in which case replacement is usually better value. When you call SPS, we'll tell you the age of your unit (from the label), what the repair costs, and what a like-for-like replacement costs. You make the call with all the information in front of you.
Can I do Rheem hot water repairs myself?
Some checks and minor maintenance are safe to do yourself (see the DIY vs Pro table above). However, any work involving the gas components of a hot water system — including the pilot, thermocouple, burner, gas valve, or gas line — must be done by a licensed gas fitter in NSW. Electric element and thermostat replacement also requires a licensed plumber or electrician. Attempting unlicensed gas or electrical work is illegal, voids your warranty, and can void your home insurance for any related water damage claims.
Does SPS service Rheem systems same day?
Yes. We carry Rheem parts in our service vehicles and can resolve most faults on the first visit. Call before 10:30am and we guarantee same-day attendance. We service all Rheem models across Sydney — storage tanks, continuous flow, solar-boosted, and heat pump systems. Call us on (02) 9072 0760 or book online.