What does replacing a hot water cylinder involve?
Why a cylinder has to be connected by a licensed plumber, and what the job actually includes.
Last reviewed 2026-09-02
Short answer on the DIY question: no. Connecting a hot water cylinder is restricted sanitary plumbing work in New Zealand. It has to be done by a licensed person. That is not us protecting our work — it is the law, and an unconsented install will not be covered by your insurance if it floods.
You can absolutely buy the cylinder yourself, though. Plenty of people buy from us and have their own plumber connect it.
What the job includes
- Draining and removing the old cylinder, and taking it away
- The new cylinder in place, with seismic restraint straps — required by the Building Code
- A new valve set: tempering valve, pressure reducing valve, expansion control valve
- Reconnecting the pipework, and the electrical side by a registered electrician
- Filling, testing and checking the temperature at the tap
Why the valves matter
They are not an upsell. A tempering valve is required so the water reaching your taps is not scalding. A pressure reducing valve protects the cylinder from high mains pressure, which is one of the most common reasons cylinders fail early. They go on every replacement.
How long it takes
A straight like-for-like swap is usually most of a day. Changing type — low pressure to mains pressure, or electric to heat pump — takes longer because the pipework and the electrical supply both change.