No hot water is one of those problems that goes from inconvenient to urgent very quickly — especially on a cold Southland morning or after a long day's work. Whether you have an electric hot water cylinder, a gas califont, a heat pump water heater, or a wetback system, there are several reasons your hot water might have stopped working, and some of them you can safely investigate yourself before calling a tradesperson.
Common Causes of No Hot Water
Understanding what might be wrong helps you describe the problem clearly to a plumber and avoid unnecessary call-out fees. The most frequent culprits include:
- Age and wear — Hot water cylinders and components deteriorate over time. Most cylinders have a lifespan of 10–15 years, and older units are more prone to element failure, thermostat faults, and corrosion.
- Weather exposure — New Zealand's climate can be harsh. Coastal homes face salt-laden air that accelerates corrosion on fittings and valves. High-UV conditions in the north degrade exposed pipework insulation, while freezing temperatures in alpine and southern regions can cause pipes to freeze or burst.
- Poor original installation or workmanship — Incorrect sizing, improper pipe connections, or a cylinder installed without meeting the NZ Building Code requirements can lead to recurring problems.
- Lack of maintenance over the years — Sediment build-up, a failed sacrificial anode, or a pressure relief valve that has never been tested are all maintenance issues that shorten system life.
- Moisture-related issues — Leaks around fittings, a weeping pressure relief valve, or condensation in poorly ventilated cupboards can cause damage to the unit and surrounding structure.
Step-by-Step: What to Check First
Before calling a plumber, run through these safe checks:
1. Check Your Power or Gas Supply
- Electric cylinder: Go to your switchboard and check whether the hot water circuit breaker has tripped. Reset it once. If it trips again immediately, do not reset it — call a licensed electrician.
- Gas califont or gas storage system: Check that your gas supply is on and that other gas appliances (e.g. the hob) are working. If you smell gas, leave the house, do not operate any switches, and call your gas supplier immediately.
2. Check the Thermostat Setting
Electric cylinders have a thermostat, usually set between 60–65 °C (as recommended to prevent Legionella growth). If it has been knocked or tampered with, it may have been turned down too low. Adjusting the thermostat on a mains-pressure cylinder is restricted work — see below.
3. Check the Pressure Relief Valve (PRV)
A constantly dripping PRV (the small valve with a pipe running to a drain) may indicate over-pressure or a faulty valve. Do not cap or remove it — it is a critical safety device.
4. Check for Visible Leaks
Look around the base of the cylinder, under sinks, and at exposed pipe joints. Even a slow drip can indicate a failing component.
5. Check Your Hot Water Timer
Many cylinders run on an off-peak timer. If the timer has lost its settings (e.g. after a power cut), the cylinder may not be heating during the hours you expect.
Types of Hot Water Systems and Their Specific Issues
| System Type | Common Faults | Key Indicator |
|---|---|---|
| Electric storage cylinder | Failed element, tripped breaker, faulty thermostat | No hot water at all, or lukewarm only |
| Gas califont (instantaneous) | Ignition failure, blocked flue, low gas pressure | Unit won't fire, error code displayed |
| Heat pump water heater | Refrigerant issue, fan fault, controller error | Error light, unusual noise |
| Wetback / solid fuel | Blocked heat exchanger, low fire output | Hot water only when fire is burning |
| Solar hot water | Pump failure, controller fault, shading | Hot water only on sunny days |
NZ Building Code and Compliance
Hot water systems in New Zealand must comply with several clauses of the NZ Building Code:
- G12 (Water supplies): Covers potable water supply and hot water delivery temperatures. Thermostatic mixing valves (TMVs) are required at certain outlets (e.g. in early childhood centres and rest homes) to prevent scalding.
- G13 (Foul water): Governs drainage of relief valve discharge.
- B2 (Durability): Materials and components must last a minimum service life.
Replacing a like-for-like hot water cylinder in the same location is generally a Schedule 1 exemption from building consent — but always confirm with your local council before starting work, as exemptions have conditions and councils can interpret them differently.
Restricted Work: What Only a Licensed Tradesperson Can Do
Plumbing and drainlaying work on hot water systems is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. This means the following must be carried out by (or under the supervision of) a licensed tradesperson registered with the Plumbers, Gasfitters & Drainlayers Board (PGDB):
- Connecting or disconnecting a hot water cylinder to the water supply or drainage
- Replacing or installing a cylinder, califont, or heat pump water heater
- Adjusting or replacing thermostats, elements, or pressure relief valves on mains-pressure systems
- Any gas work on a gas water heater
Electrical connections to a hot water cylinder (the wiring from the switchboard) are restricted electrical work and must be done by a registered electrician — see the Electrical Workers Registration Board (EWRB).
What a homeowner can safely do: Check the switchboard, reset a tripped breaker (once), check the timer, and visually inspect for leaks. Everything beyond that should involve a professional.
Prevention and Maintenance
Regular maintenance is the best way to prevent hot water failures and extend the life of your system. Include the following in your seasonal home maintenance checklist:
- Annual: Have a licensed plumber check and manually operate the pressure relief valve, inspect the anode rod (sacrificial anode), and check all visible connections for corrosion or weeping joints.
- Every 5 years (or per manufacturer guidance): Replace the sacrificial anode in a storage cylinder — this is the single most effective way to extend cylinder life.
- Insulate pipes: In colder regions (Canterbury, Otago, Southland, central North Island), insulate exposed hot and cold water pipes to prevent freezing and reduce heat loss.
- Check your timer settings after any power outage.
- Flush sediment from the base of older cylinders periodically — your plumber can advise on frequency based on your local water quality.
BRANZ provides research-backed guidance on building maintenance that is well worth bookmarking for NZ homeowners.
When to Call a Professional
Call a licensed plumber if:
- The problem is recurring or you cannot identify the cause after basic checks
- There is water pooling around the cylinder or under the floor
- The pressure relief valve is continuously discharging
- The cylinder is more than 10–12 years old and losing performance
- You need any component replaced or any pipe disconnected
- The problem is affecting the structure of your home (e.g. water damage to framing or linings)
Call a licensed gasfitter (also registered with the PGDB) for any fault on a gas califont or gas storage system.
Call a registered electrician if the circuit breaker keeps tripping or if there are any signs of electrical faults near the cylinder.
A qualified local tradesperson can diagnose the root cause, carry out the work legally, and issue the required Certificate of Compliance (CoC) — which is important for your insurance and for future property sales. You can find licensed plumbers and gasfitters in your area on tradedirectory.co.nz.
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