Signs a replacement is on the cards
- Water seeping from the cylinder body itself, not from a valve or a pipe joint.
- Rusty or discoloured water from the hot taps but not the cold.
- A repair bill that would be a big share of what a new cylinder costs.
- The household has outgrown it and the hot water runs out every evening. Our sizing guide helps here.
- You already want something different: mains pressure, a heat pump or gas continuous flow.
What a plumber will do
A plumber will start with the label on the old cylinder: its type, capacity, pressure and heat source. Then they look at the pipework, the valves, the cupboard or outdoor spot, and how the cylinder is held in place.
Once you've agreed on the new one, they isolate and drain the old cylinder, take it out, then fit, restrain and plumb the replacement and commission it. An electrician makes the electrical connection on an electric or heat pump cylinder. On gas, an authorised gasfitter connects the gas.
Makers set out what their cylinders need. Rheem's All Pressure installation guide, for example, lists a safe tray, seismic restraints and a cold water expansion valve. Ask what your new model's maker requires and get the plumber to point each one out.
This page sits under our main hot water cylinders guide, which covers every cylinder type.
What changes a replacement
| What it usually means for the job | |
|---|---|
| Same type, same spot | The most straightforward version. It is still restricted plumbing work, and it still has to meet the Building Code. |
| Low pressure to mains pressure | Possible in some homes and not others. The plumber decides after looking at your pipes and fittings. See mains pressure cylinders. |
| Electric to heat pump | Rheem notes a heat pump needs outdoor space, so the cylinder may have to move. See heat pump hot water. |
| Gas storage to gas continuous flow | Rheem says continuous flow needs a larger gas pipe from the meter than most storage heaters. See califonts. |
| A cylinder fed by a wetback | A different consent clause applies (clause 37). See wetbacks. |
| Moving it to a new spot | The Building Act treats repositioning alongside replacement, but new pipe runs and access add work. |
Consent, licences and the law
Building work needs a building consent unless the Building Act exempts it. For water heaters, the exemptions are Schedule 1 clauses 36 to 38. Clause 38 covers replacing a water heater, including repositioning an existing one, when the replacement is connected to, or incorporates, a controlled heat source.
That exemption only counts when the work is done by a person authorised under the Plumbers, Gasfitters, and Drainlayers Act 2006. A homeowner relying on the householder exemption does not qualify. Exempt or not, the finished installation must comply with the Building Code. The Act text we read doesn't define 'controlled heat source', so let the plumber or the council confirm your new cylinder fits.
Unauthorised plumbing carries a fine of up to $10,000, and knowingly paying someone unauthorised to do it is an offence as well. In April 2026 the PGDB reported an $8,000 fine for illegal plumbing and drainlaying at five properties, one of them a hot water cylinder installation. Our consent guide goes further.
Your part, and theirs
You can
- If it's leaking, turn the cylinder off at the switchboard (or turn the gas off) and close the cold supply valve.
- Photograph the label, the valves and the space around the cylinder.
- Measure the cupboard or outdoor spot if you're thinking of a different size or type.
- Note how many people use hot water and when it runs short.
- Search the plumber's own first and last name on the PGDB register.
Leave to an authorised tradie
- Draining, disconnecting and removing the old cylinder.
- Fitting, restraining and plumbing in the new one.
- Valves, the safe tray and any pipework changes.
- The electrical connection (an electrician) or the gas connection (an authorised gasfitter).
Questions to ask before you say yes
- Which type and size do you recommend for us, and why that one?
- Does this job fit the clause 38 exemption, or will it need a consent?
- Who will make the electrical or gas connection?
- Is your practising licence current, and who is your certifying supervisor, if you have one?
- What documents will I receive when the work is completed?
- Is this a quote or an estimate?
What we would do
If the tank itself is leaking, don't spend money on parts. Use the breakdown to decide what you want for years to come: the same again, mains pressure, a heat pump or a califont. Have a cylinder replacement specialist look before you pick, because your pressure, space and pipework decide what's practical.