Water Hammer After a New Shower Mixer? Here’s What’s Happening
water hammer after new shower mixer: Just renovated and now your pipes bang every time you shut the shower? Here's…
No Hot Water? A Troubleshooting Guide Before You Call a Plumber
No Hot Water? A Troubleshooting Guide Before You Call a Plumber, a Prime Plumbing & Gasfitting plain-English guide to no hot water troubleshooting for Melbourne homeowners. Below we cover what works, what doesn't, and when to call a licensed plumber.
Quick answer: Before you call a plumber, run through these checks. Gas units: confirm the gas is on (try a gas cooktop), check the pilot light is lit if it's an older unit, look for a fault code on the controller. Electric units: check the circuit breaker hasn't tripped, press the thermostat reset button if accessible, check the isolation switch hasn't been knocked. Heat pumps: check power, look for an error code, check the air intake isn't blocked. Tank units: confirm the cold water inlet valve is open. If none of these recover hot water within 30 minutes, you've got a real fault, call a licensed plumber. Don't open the unit casing or attempt internal repairs.
Before you start: rule out the simple stuff
Most "no hot water" calls turn out to be one of about six causes, and three of them you can check yourself in five minutes. Before you spend money on a callout, run through these checks in order.
1. Is the cold water working?
If neither hot nor cold is running at the tap, you've got a water-supply problem, not a hot-water problem. Check:
- Other taps in the house, is anyone getting water?
- Stop tap at the meter, is it on?
- Have you been disconnected (paid bills, council works, etc)?
- Has there been a frozen pipe overnight? (Rare in Melbourne but possible in winter)
Confirm cold water is flowing at multiple fixtures before assuming the hot water unit is the problem.
2. Is hot water working at one tap and not another?
If hot is working at, say, the kitchen sink but not the bathroom shower, the hot water unit is fine, the problem is downstream. Possible causes:
- Tempering valve at the unit drifted (delivers cold instead of mixed)
- Mixer cartridge in the affected tap is faulty
- Isolation valve under the basin or cistern has been turned off
- Hot supply line frozen or blocked between unit and fixture
This is a different problem from a unit fault. Skip to the tempering valve troubleshooting section below.
3. Is hot water working but running cold quickly?
If you get hot water for 30 seconds and then it runs cold, the tank is empty and not refilling/heating fast enough. Possible causes:
- Recent high demand (just had a bath, washing machine ran on hot)
- Element failure (electric)
- Burner issue (gas)
- Heat pump in defrost cycle
- Tank capacity smaller than current demand
This needs a service visit, but it isn't usually an emergency. A unit that recovers in 1-3 hours after a big drain-down is normal. A unit that never recovers needs attention.
Gas hot water troubleshooting
Gas storage units
- Check the pilot light (older units only). The pilot is a small flame at the base of the unit, visible through a sight-glass or small window. If the pilot is out, follow the relighting instructions on the unit's label, typically: turn the gas knob to PILOT, hold the ignition button, light the pilot, hold the gas knob in for 30 seconds, release, set the knob to ON.
- Check for a fault code on units with electronic controllers. Most modern units have a small LED display or status light. Fault codes vary by brand, consult the manual or quick-reference panel on the unit. A "no flame" or "ignition fault" code points to gas supply, igniter, or thermocouple issues.
- Confirm gas supply by trying a gas cooktop or other gas appliance. If nothing else gas-powered is working, you've got a gas-supply problem (gas off at the meter, regulator fault, distributor outage), not a hot water unit problem.
- Check the unit isolation valve at the gas line going into the unit. Make sure it's open (lever in line with the pipe).
If the pilot won't stay lit after multiple attempts, or the unit shows a fault code that won't clear, you've got a real fault, call a licensed gasfitter. Most likely a failed thermocouple, igniter, or gas valve.
Gas instantaneous (continuous-flow)
- Check the controller: most have a digital display. A fault code or no display means power is out or the controller has failed.
- Check the gas supply at another gas appliance.
- Check water flow: instantaneous units need a minimum flow rate to fire the burner. If the tap isn't fully open or the inlet filter is blocked, the unit may not ignite. Try opening the hot tap fully.
- Check the inlet water filter if you can access it. Sediment can clog the filter and starve the unit of flow.
- Check the fan: modern instantaneous units have a flue fan. If you don't hear it spin up when you open the hot tap, the controller, fan or sensor has likely failed.
If the controller shows a fault code that won't clear, call a gasfitter.
Electric hot water troubleshooting
Electric storage
- Check the circuit breaker at the switchboard. Hot water units usually have a dedicated breaker, sometimes labelled "HWS" or "Hot Water". If it's tripped, reset it once. If it trips again immediately, stop: there's an electrical fault and you need a licensed electrician/plumber.
- Check the isolation switch near the unit. Some installations have an external switch you can confirm is ON.
- Check the thermostat reset button if accessible. Many electric storage units have a small red reset button on the thermostat that pops out if there's an over-temperature event. Pressing it back in restarts the unit. If it pops out again within hours, the thermostat or element has failed.
- Check the off-peak tariff if your unit runs on controlled load. If you've been disconnected from off-peak, the unit only heats during off-peak hours and might be empty during the day. Check with your retailer.
- Listen for the element: if the unit is supposed to be heating, an electric element is silent (you won't hear it) but the tank may make a slight tick or pop sound as it warms. Touch the side of the tank above the element, if it's warming up, the element is working. If it's cold even when the unit should be heating, the element has failed.
Heat pump
- Check power at the unit and at the switchboard breaker.
- Look for an error code on the controller. Common codes include refrigerant pressure errors, fan errors, sensor errors.
- Check the air intake isn't blocked: leaves, dust, snow, or anything covering the fan inlet will stop the unit from drawing in air. Clear any obstruction.
- Check the unit isn't in defrost cycle: heat pumps periodically defrost the outdoor coil in cold weather, during which they don't heat. Wait 30 minutes and check again.
- Check the timer/schedule: if your heat pump is scheduled to only heat during specific hours (often to align with solar) and you're outside that window with no stored heat, you'll see no hot water until the next scheduled run.
If the heat pump shows a persistent error code or won't recover, call a licensed plumber.
Tempering valve troubleshooting
A tempering valve at the hot water unit can drift, particularly older valves more than 5-10 years old. Symptoms: hot water is "less hot than it used to be" rather than completely absent.
If you suspect this:
- Check the unit's tank temperature setpoint (should be 60-65 °C)
- The tempering valve set point should deliver around 50 °C at the most distant tap
- Adjustment of the tempering valve is regulated work, book a licensed plumber to verify and adjust
Don't adjust the valve yourself. Tempering valves are deliberately designed to need calibrated measurement; a homeowner adjusting up "to make the shower hotter" is how children get scalded.
Book a hot water diagnosis
Call 0475 407 670 during business hours or send through the contact form. Tell us your unit type (gas/electric/heat pump), age, and what symptoms you're seeing, we'll often have a good idea of the diagnosis before we arrive.
- BPC #103414: Building and Plumbing Commission licence
- Type A gasfitting endorsement for gas appliance work, held on the BPC licence
- 4.8 stars on Google
- Fixed-price written quote before any work
When you've ruled everything out
If you've worked through the relevant checks and hot water hasn't returned, you've got a real fault. The most common diagnoses we see:
- Failed thermocouple (gas storage), typically $150-$300 to replace
- Failed thermostat or element (electric storage), typically $200-$450 to replace
- Failed igniter or gas valve (gas instantaneous), typically $250-$500 to replace
- Failed compressor or refrigerant leak (heat pump), typically more involved repair
- Tank corrosion / leak (storage units, often at end of life), replacement is usually the answer
- Tempering valve drift: typically $300-$550 supply and fit replacement
For end-of-life units (10-15+ years old), replacement is normally more sensible than repair, a fresh unit gives you another decade of reliability and often comes with a manufacturer warranty.
Service area
Prime Plumbing & Gasfitting services hot water repairs across Melbourne's eastern, south-eastern, inner-east and bayside suburbs. See all suburbs we service
When to call a licensed plumber
The Victorian Building Authority maintains a plumbing licence search so you can verify your plumber is licensed.
Frequently asked questions
It depends on the noise. Tank rumbling/percolating is typically sediment buildup at the bottom of the tank, not an emergency, but it shortens life. Hissing or boiling sounds can mean a relief valve issue or thermostat fault, get it checked soon. Banging during operation is often water hammer from upstream, not a unit fault.
For an electric storage unit on full mains power: 1-3 hours after reset, depending on tank size. For an electric unit on off-peak: only during the next off-peak window, typically overnight. For a gas unit: 30-60 minutes after the unit re-fires. For a heat pump: 2-5 hours depending on tank size and ambient temperature.
Yes, cold supply isn't affected by a hot water unit fault. You can flush toilets, run the washing machine on cold, and use cold-only taps normally.
If your unit is more than 10-12 years old and you're already paying for a callout, replacing often makes sense. Repair on an old unit often buys 1-3 years; a new unit gives you a decade plus warranty. We'll quote both options at diagnosis.
No, turning off gas or power to the unit is safe for short periods. For longer absences (e.g. holiday) it's fine to leave it off; for a tank unit, it'll cool but won't damage anything. Just remember to turn it back on at least 1-3 hours before you need hot water.
Most often a faulty thermocouple (the safety device that holds the pilot gas valve open). Other causes: drafts at the pilot location, blocked pilot orifice, low gas pressure, or a faulty pilot generator on newer electronic-pilot units. A gasfitter can diagnose in one visit.
No, element replacement requires draining the tank, isolating power, and re-commissioning the unit. It's regulated electrical and plumbing work that needs a licensed plumber. Cost-wise, the part is cheap; the labour and the safety check are what you're paying for.
How much does the repair cost?
Indicative ranges only, actual cost depends on diagnosis, part availability, and access:
- Diagnostic callout: typically $150-$250 (often credited toward repair if you proceed)
- Thermocouple replacement (gas): typically $250-$400 supply and fit
- Element / thermostat replacement (electric): typically $300-$550 supply and fit
- Igniter / gas valve (instantaneous): typically $400-$700 supply and fit
- Like-for-like replacement of end-of-life unit: typically $1,800-$3,500 (gas) / $5,500-$8,500 before rebates (heat pump)
We always quote in writing first. For unit replacement, our hot water replacement service page has details.
- When did the issue start?
- Is it isolated to one fixture or multiple areas?
- Are there any visible leaks, smells or unusual sounds?
- Have you turned off the relevant isolation valve?
- Hot water systems Melbourne: diagnostics, repair, and new installs
- Hot water replacement Melbourne: like-for-like and upgrade replacements
- Gas fitter Melbourne: for gas-side service and repair work
