Hot water gone cold? How to tell if it's a plumber or electrician
Most homeowners default to calling a plumber when hot water dies. Often it's the electrical side that's failed. Here's a 30-second diagnostic to tell which.
Most people default to calling a plumber when the hot water dies. Half the time it’s the electrical side that’s failed and a plumber can’t help. Here’s how to tell which trade you actually need before you book anyone.
Safety first
Before you start diagnosing, check these three things:
- If you smell burning at the cylinder, turn off the power at the switchboard immediately and call us on 09 392 0055.
- If water is leaking from the cylinder, turn off the water at the mains first, then call a plumber.
- If neither of those, follow the diagnostic below.
The 30-second diagnostic
Touch the pipe at the top of the cylinder. Not the cylinder itself, the pipe coming out of the top. That one pipe tells you most of what you need to know.
| What you find | Likely cause | Who to call |
|---|---|---|
| Cold pipe | Element or thermostat failure | Electrician |
| Warm pipe but cold water at the tap | Tempering valve issue | Plumber first |
| Hot pipe but no hot water at any tap | Tempering valve issue | Plumber |
| Hot pipe but no hot water at one tap only | Tap or pipe issue at that fixture | Plumber |
| Cylinder making clicking, popping or banging sounds | Element scaling or ageing | Electrician to check the element first |
| Switchboard breaker keeps tripping when hot water comes on | Element shorted out | Electrician, urgently |
| No power to the cylinder switch | Wiring or switch issue | Electrician |
If the pipe is cold and the breaker hasn’t tripped, it’s almost always the element or thermostat. Both are electrical components. A plumber can’t fix either.
What an electrician does for hot water cylinders
- Tests the element with a multimeter to see if it’s still functional
- Replaces the element if it’s failed
- Replaces the thermostat
- Checks the wiring from the switchboard down to the cylinder
- Checks the cylinder isolator switch on the wall
- Fault finds the circuit if the breaker keeps tripping
On most residential cylinders these are straightforward jobs. Element and thermostat replacement in one visit is common.
What a plumber does
- Replaces the cylinder itself
- Fixes leaking valves and pipe connections
- Replaces tempering valves (the valve that mixes hot and cold to a safe outlet temperature)
- Sorts water pressure issues
- Replaces sacrificial anode rods
- Does whole-cylinder replacements
Plumbers don’t touch the element or thermostat. Those are electrical.
When you need both
Some jobs cross over. A new cylinder install needs a plumber for the water connections and an electrician for the power. A cylinder replacement where the wiring is old often needs both trades too. Don’t pay for two separate callouts if you can avoid it.
If we come out to your place and find the job needs a plumber as well, we’ll tell you up front and we work with a few good plumbers in South Auckland we’re happy to recommend. Getting both trades lined up on the same day or close together saves you money and downtime.
When to repair vs replace
If your cylinder is over 15 years old and the element fails, it’s often worth replacing the whole cylinder rather than the element alone. Elements that fail repeatedly on an older cylinder suggest the tank itself is on borrowed time. We’ll tell you straight what’s worth fixing and what’s worth replacing. There’s no point putting a new element into a cylinder that’ll need replacing next year anyway.
Signs your cylinder is near end of life:
- Over 15 years old
- Visible rust on the outer casing
- Leaking from anywhere other than a valve
- Repeated element or thermostat failures
- Hot water running out unusually quickly
FAQs
Hot water cylinder making popping noises - is it dangerous? Not immediately dangerous, but it’s a sign something’s wrong. The usual cause is scale buildup on the element, which makes it work harder and shortens its life. Get it checked. If it’s combined with a burning smell or tripping breaker, stop using it and call us today.
Can I replace a hot water element myself? No. Any work on a hard-wired fixed appliance is restricted to licensed electrical workers in New Zealand. It’s also not worth the risk. The element sits inside a tank of water under pressure, and replacing it wrong can cause leaks, shocks, or worse. An electrician can swap an element in under an hour.
How long should a hot water cylinder last? A standard electric cylinder usually lasts 15 to 20 years. Some go longer with good water quality and regular anode rod replacement. Hard water areas (which most of South Auckland isn’t, but worth checking) shorten cylinder life.
Why does my hot water run out so quickly? A few possibilities: the cylinder is undersized for the household, the thermostat is set too low, the element is part-failed and heating slowly, or scale buildup has reduced capacity. An electrician can test the thermostat and element. If those are fine, the cylinder itself may need upsizing, which is a plumber’s job.
Does a leaking cylinder need replacing? Usually yes. Leaks from the body of the tank (not the valves or connections) mean the tank has corroded through, and there’s no safe repair. A plumber will replace the cylinder. If you catch it early, before water damage spreads, replacement is far less painful.
If your pipe is cold, give us a call on 09 392 0055. We’ll diagnose the issue, tell you straight what’s going on, and quote you before any work starts.
Arahia Electrical covers South Auckland - Manurewa, Papakura, Manukau, Ōtara, Māngere, Pukekohe, Flat Bush and wider Auckland.