Hot Water Cylinder Repairs
From leaks to no hot water, we offer fast NZ wide diagnosis to repair or replace hot water cylinders.
No Hot Water At All
Waking up to a cold shower is usually the first sign something’s wrong. Before calling anyone, check your switchboard for a tripped breaker and make sure your hot water cylinder switch is on, this alone explains a large share of “no hot water” calls.
If your cylinder is fairly young and you’re in the city, a total loss of hot water can also be caused by the ripple relay rather than a fault with the cylinder itself. Power companies use these to control off-peak heating, and a stuck relay can cut power entirely, worth a quick call to your power company before booking a repair.
Once you’ve ruled those out, a total loss of hot water on electric cylinders is usually electrical rather than a tank fault, a blown element or thermostat that’s stopped switching on. As long as there are no leaks, that’s an electrical fault, not a sign the tank has failed. Gas and continuous flow units can lose hot water due to an ignition fault, gas supply issue, or a sensor error on the display.
No hot water doesn’t automatically mean a new cylinder — in most cases it’s a repairable electrical or component fault.
For older cylinders, though, replacing can be the smarter move — a thermostat or element repair on an aging tank often becomes an annual fix.
Weak or Low Hot Water Pressure
If your hot water dribbles out while the cold tap runs fine, the cause usually sits with the cylinder or its fittings rather than your home’s water supply. Pressure complaints are common after moving into a new home or upgrading tapware during renovations, so it’s worth checking if the issue started around then.
Older low pressure cylinders are simply built to deliver less flow than a mains pressure system, so if yours has always been weak, that may just be its design. If you’re on tank water, that doesn’t rule out an upgrade, a site visit can still confirm whether mains pressure is suitable for your setup, since hot water can come out just as fast as cold.
A sudden drop in pressure, however, points to sediment build-up inside the tank, a partially blocked pipe or valve, or a failing pressure-reducing valve on a mains pressure unit. We can diagnose which of these applies and, where a low pressure system is holding your household back, talk you through upgrading to mains pressure. If the cylinder is already old, it’s often best to skip the repair and go straight to replacement.
A sudden pressure drop is a fixable fault; a cylinder that’s always been weak may simply need a mains pressure upgrade.
Rusty, Discoloured or Smelly Hot Water
Discoloured or metallic-smelling hot water is one of the clearest warning signs a cylinder is corroding internally, particularly once a unit passes the 10–15 year mark. To narrow down the cause, run your cold tap first — if it’s clear — then run the hot tap on its own. If only the hot water is affected, the issue is almost always inside the cylinder itself, often linked to a worn-out sacrificial anode that’s no longer protecting the tank from rust. If both taps are affected, the problem is more likely in your home’s pipework rather than the cylinder. Either way, this is a sign that shouldn’t be left unchecked, as internal corrosion is what eventually leads to a tank leak.
Discoloured hot water (with clear cold water) usually means internal corrosion — an early warning before a leak develops.
Strange Noises From the Cylinder
Banging, knocking, hissing or popping sounds coming from your hot water cylinder are never normal and shouldn’t be ignored. These noises are typically caused by sediment and mineral deposits settling at the base of the tank, which trap water beneath the heating element and cause it to boil and pop as steam bubbles escape. Less commonly, the noise can point to a valve under strain or a heating element starting to fail. Left unaddressed, sediment build-up reduces efficiency, shortens the cylinder’s lifespan, and can eventually damage internal components.
Odd noises are almost always sediment build-up — a maintenance issue now that can become a bigger repair later.
Inconsistent or Fluctuating Water Temperature
Showers that swing between hot and cold, or hot water that never quite reaches the temperature you expect, usually trace back to a thermostat that’s lost accuracy, sediment insulating the heating element from the water it’s meant to heat, or a tempering valve that needs adjusting. In New Zealand, tempering valves are commonly fitted to limit water to a safe temperature, so a valve fault can just as easily present as water that’s too cool rather than too hot. Because a handful of different components can cause the same symptom, this is one repair best diagnosed on site rather than guessed at.
Fluctuating temperature is rarely one single cause — a proper inspection saves you paying to replace the wrong part.
Hot Water Running Out Too Quickly
If your cylinder used to see the household through back-to-back showers and now runs cold halfway through, sediment build-up reducing the tank’s effective capacity is the most common culprit. A faulty element that’s only partially heating the tank, or a thermostat set lower than it should be, can produce the same effect. It’s also worth checking whether household hot water demand has simply grown — a bigger family, a new bath, or an added appliance can outpace a cylinder that was previously adequate, in which case an upsized tank rather than a repair may be the better long-term fix.
Cylinder getting old and not meeting your new requirements — sediment build-up or a fault is usually the cause, not necessarily extra demand.
Faulty Valves, Elements & Thermostats
Many hot water cylinder callouts come down to a handful of repairable components rather than the tank itself. Heating elements wear out and stop heating water efficiently; thermostats drift out of calibration or fail electrically; and valves — including the pressure relief, tempering and non-return valves — can stick, corrode or fail to seal properly over time. These are generally straightforward and cost-effective to replace on a cylinder that’s otherwise in good condition, which is why we always check component-level faults before recommending a full replacement.
Elements, thermostats and valves are the most common cylinder repairs — and usually the most affordable to fix.
Overflowing or Constantly Discharging Cylinder
A cylinder that keeps discharging water — sometimes visible as a steady trickle from an overflow pipe outside the house — is often mistaken for a minor issue because the water can feel cool by the time it reaches the ground. Some dripping is actually normal: water expands by up to 3% as it heats, which is around 5.4L in a 180L cylinder, and that extra volume has to go somewhere via the vent pipe or relief valve.
Here’s a quick way to tell the difference: turn off power to the tank for a few minutes. If the dripping stops, it’s just thermal expansion doing its job. If it keeps going, the valve is likely faulty and continuously venting hot water — which quietly drives up your power bill while wasting water.
The cause is typically a faulty pressure relief or pressure-reducing valve, excess pressure in the system, or a valve that’s never been serviced. Manufacturers generally recommend testing the pressure relief valve every six months; if no water flows when it’s tested, that’s a sign it needs professional attention straight away. Any valve we replace is backed by Apex’s 5-year warranty on parts and labour.
A cylinder that’s constantly discharging is wasting hot water and money, even if the water feels cold by the time you notice it.
Repair or Replace?
Not every hot water cylinder problem means starting again with a new unit. As a rule of thumb, cylinders under 10 years old are almost always worth repairing, and even those between 10 and 15 years old often have life left in them once a fault is fixed. Replacement becomes the more sensible option once a cylinder is leaking from the tank itself (rather than a valve or fitting), heavily corroded internally, past the 15-year mark, or requiring repeat call-outs for different faults. We’ll always give you a straight answer on which side of that line your cylinder sits, and a fixed price either way.
Under 10 years old, repair is usually worthwhile. A leaking tank, heavy corrosion, or an age of 15+ years generally points to replacement.
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