Guidance on replacing existing cylinders

Any new HWC installation must comply with the requirements of the New Zealand Building Code (NZBC).

The uncertainty arises when replacing existing cylinders, where the existing cylinder has no safe tray. NZBC G12/AS1 5.2.3 Safe trays says:

Performance E3.3.2: states that "Free water from accidental overflow from sanitary fixtures or sanitary appliances must be disposed of in a way that avoids loss of amenity or damage to household units or other property. An acceptable method of preventing water damage is to locate a safe tray below the water tank (see Figure 14). The safe tray shall incorporate a drain with a minimum diameter of 40 mm. Where the tank overflow discharges into the safe tray, the diameter of the safe tray drain shall be greater than the overflow pipe from the tank and comply with Paragraph 5.2.2.

Clause 42A(2) of the Building Act 2004 outlines that existing work cannot be any less compliant than before the work began. This essentially means when replacing a HWC, if it did not have a safe tray beforehand, it is not always mandatory to install a safe tray.

However, the Board recommends it is best practice is always to install a safe tray. The NZBC G12/AS1 also has further requirements that are relevant to whether a safe tray should be installed:

6.11 Water heater installation

6.11.1 Water heaters shall be installed in accordance with the manufacturer's instructions.

6.11.2 Where heating units, sacrificial anodes, thermostats, pipework connections, valves, or other accessories being components of a storage water heater are installed, they shall be accessible for inspection, maintenance and removal.

6.11.3 Storage water heaters shall have:

a) Safe trays complying with Paragraph 5.2.3

b) Connections compatible with the pipe material used, and

c) Drain pipes (for every storage water heater of more than 45 litres capacity) which:

i) have a conveniently located isolating valve, and terminate with a cap or plug suitably located to easily empty the vessel for maintenance, or

ii) terminate outside the building with a cap only.

Many major HWC manufacturers include in their installation instructions that a safe tray must be installed. This means the requirement that water heaters shall be installed in accordance with the manufacturer’s instructions cannot be overlooked.

Should any failure occur and damage be caused to any part of the structure or components of the building, it is likely the manufacturer would not cover any damage that arose as a result of the installation instructions not being followed. It is also possible the homeowners insurance would be unwilling to cover property damage should a leak occur where a safe tray was not installed and this may be something to advise homeowners of when discussing with them the need for a safe tray if one wasn't previously installed.

In November 2023 there was an amended to NZBC G12/AS1 which provides greater flexibility in seismic restraint locations so not to clash with the safe tray.