Hot water cylinder maintenance: what to check each year

Your hot water cylinder is one of the hardest-working appliances in your home — quietly heating water day and night, often for years without a second thought. But like any appliance, it needs regular attention to stay safe, efficient, and long-lasting. Neglecting basic maintenance can lead to costly failures, water damage, or even dangerous pressure build-up. This guide walks NZ homeowners through what to check each year, season by season.

Why annual maintenance matters

NZ's climate throws a lot at our homes — humid summers in the north, cold frosty winters in the south, and coastal salt air that accelerates corrosion. Hot water cylinders (whether electric, gas, or heat pump) are vulnerable to all of these. A well-maintained cylinder can last 15–20 years or more, while a neglected one may fail in under a decade.

Regular checks help you:

• Catch small problems before they become expensive repairs
• Maintain energy efficiency and keep power bills down (see Energywise for tips on hot water energy use)
• Ensure safety valves and fittings are working correctly
• Stay compliant with the NZ Building Code, particularly G12 (Water Supplies), which sets requirements for hot water systems

Understanding your cylinder: a quick overview

Most NZ homes have one of the following:

Knowing your cylinder type helps you understand which checks apply to you.

Your annual maintenance checklist

Some of these tasks are safe for a competent homeowner to do. Others — particularly anything involving gas connections, electrical wiring, or pressure relief valve replacement — are restricted work under NZ law and must be carried out by a licensed professional.

Safety first

Never tamper with gas fittings or electrical connections yourself. Gas work must be done by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). Electrical work on the cylinder's wiring or element must be done by a registered electrician (EWRB). Plumbing work on the cylinder itself — including valve replacement — must also be done by a licensed plumber.

What homeowners can check themselves

• Inspect the cylinder exterior — Look for rust, damp patches, or corrosion on the tank body and surrounding pipes. Any moisture on or around the cylinder warrants a closer look.
• Check the area around the cylinder — Ensure there's adequate ventilation and no stored flammables nearby (especially important for gas units).
• Listen for unusual noises — Rumbling, popping, or banging can indicate sediment build-up inside the tank.
• Check the temperature setting — The recommended storage temperature is 60°C or above to prevent Legionella bacteria growth, as noted by BRANZ. Check your thermostat dial if it's accessible.
• Inspect the pressure relief valve (TPR valve) drain pipe — This pipe should run to a safe discharge point (outside or to a drain). Make sure it isn't blocked, kinked, or discharging constantly (constant dripping means the valve or system pressure needs professional attention).
• Look for signs of the TPR valve weeping — A small amount of occasional dripping is normal as pressure releases, but continuous flow is not.
• Check pipe insulation — Particularly on pipes in cold areas like garages or under-floor spaces. Foam pipe lagging is inexpensive and available at Bunnings or Mitre 10.
• Clear debris from heat pump units — If you have a heat pump water heater, keep the air intake area clear of dust, leaves, and lint.

Tasks for a licensed plumber (annual service)

• Test the TPR (temperature and pressure relief) valve — A plumber will manually lift the lever briefly to confirm it opens and reseats correctly. A faulty TPR valve is a serious safety risk.
• Check the anode rod — Most cylinders have a sacrificial magnesium anode rod that protects the tank lining from corrosion. It should be inspected every 3–5 years and replaced when significantly depleted. This is especially important in areas with aggressive water chemistry.
• Flush sediment — In areas with harder water, sediment can accumulate at the base of the tank, reducing efficiency and causing noise. A plumber can flush this out.
• Inspect all valves and fittings — Including the cold water inlet valve, expansion valve, and any isolating valves.
• Check the element (electric cylinders) — A plumber or electrician can test the heating element for efficiency and signs of failure.
• Gas burner inspection — For gas cylinders, a licensed gasfitter should inspect the burner, flue, and connections annually.

Season-by-season reminders

• Autumn (March–May): Before winter demand increases, book a professional service. Check pipe insulation in exposed areas.
• Winter (June–August): In frost-prone regions (Central Otago, Canterbury foothills, Waikato highlands), check that outdoor pipes and fittings are protected. Monitor your cylinder for any changes in performance.
• Spring (September–November): Inspect the cylinder exterior after winter. Clear any debris from heat pump intakes. Check the TPR valve drain pipe is clear.
• Summer (December–February): Consider whether your thermostat setting is still appropriate. Solar hot water systems may need a check on the collector panels and connections after UV-intense summer months.

Common mistakes homeowners make

• Ignoring a dripping TPR valve — This is often a sign of excess system pressure or a failing valve. Left unattended, it can become dangerous.
• Setting the temperature too low — Temperatures below 60°C can allow harmful bacteria to multiply. Don't turn it down too far to save power.
• Skipping the anode rod — Many homeowners don't know this component exists. A depleted anode rod leads to tank corrosion and premature failure.
• DIY gas or electrical work — This is illegal and dangerous. Always use a licensed tradesperson.
• Ignoring rust or moisture — Early signs of corrosion or leaks are easy to dismiss but can lead to a full cylinder failure and significant water damage.

When to call a professional

Call a licensed plumber if you notice:

• Any water pooling around the cylinder base
• The TPR valve dripping constantly
• Discoloured or rusty hot water
• Reduced hot water pressure or volume
• Unusual noises from the tank
• The cylinder is more than 15 years old and hasn't been serviced

Call a licensed gasfitter for any gas-related concerns, and a registered electrician for electrical faults. You can find qualified local tradespeople at tradedirectory.co.nz.

For guidance on what work requires a licensed building practitioner, visit LBP or MBIE Building Performance.

Sources & further reading

• BRANZ — Hot water systems guidance
• Energywise — Hot water and energy efficiency
• MBIE Building Performance — NZ Building Code
• PGDB — Licensed plumbers and gasfitters
• EWRB — Registered electricians
• Consumer NZ — Hot water cylinder advice