Rinnai Infinity Hot Water Unit

Firstly – All plumbing and electrical work should only be completed by licenced tradespeople, and be done in compliance with the relevant Australian industry standards.

The most common are Gas Hot Water Systems are storage units (larger cylinders), however, continuous flow units are also becoming a popular choice for homeowners. Continuous Flow units are smaller, can go places where storage units can’t be fitted, are more efficient and also don’t run out of hot water.

Unit Location

If this is a new installation, the location of the unit needs to be considered so it is as close as possible to the outlets. If it is the replacement of an existing unit, then you need to consider if the replacement unit will fit where the current one exists (for example, into a cupboard). 

If the hot water unit is located indoors then it may need a safe tray under it, with timber slats required to be installed between the unit and the safe tray. A drain to the outside or a Mildred Valve is also fitted, this valve will shut off the water in the event of water leaking from the unit. It is also important that the ventilation and flue requirements are correct if the installation is indoors.

If the hot water unit is installed outside, then it is installed on a concrete slab and the clearance requirements to openings into the building, from corners, eaves, etc. need to be considered.

Connecting the Unit

For unit replacements, you will also need to consider whether the existing installation and associated connections will need to be altered to fit your replacement unit. A qualified plumber will be able to advise you on this.

A gas pipe needs to be connected either into the existing piping OR back to the meter, depending on the existing pipe size and the megajoule rating of the new unit. This is to make sure that the new hot water unit will operate correctly with all of the existing gas appliances running at the same time. The gas installation needs to be pressure tested as per the relevant compliance standards to ensure that it is gas-tight and there are no gas leaks. The new pipes also need to be clipped as per the relevant standards.

The hot and cold water pipes are connected to the unit. Depending on the type of unit, either a duo valve or a ball type isolation valve is fitted.

The cold water pressure needs to be tested and a limit valve may need to be fitted (a pressure reduction valve fitted at the outlet of the water meter is best). A cold water expansion valve fitted to the inlet side of a mains pressure unit also has great benefits in reducing the pressure inside the unit’s cylinder and may help to extend the life of the pipes, taps and appliances in the building.

A drain is run off the PTR valve to the outside, to comply with the relevant standards. There are clauses as to how far the drain can run in certain sizes, depending on the number of bends, where and how the drain is to terminate, etc. Again, an experienced plumber will be able to complete work in accordance with these standards

A tempering valve may also need to be fitted, which stops the temperature of the hot water from exceeding 50°C to any ablution fixtures, like the bathroom for example.

Commissioning the Unit

To finish up the installation job, the new hot water system needs to be commissioned to ensure that it operates correctly. This involves carrying out a burner pressure test, adjusting the pilot and the main burner aeration. If a tempering valve is fitted, then after the water temperature is reached, the tempering valve needs to be set to 50°C.


As you can see installing a Gas Hot Water unit is quite a complex job and should be left to the professionals. The team at O’Shea Plumbing are ready to help you with all of your hot water unit installations, replacements or repairs. Call the plumber Melbourne locals have been trusting for years – call us on (03) 9888 2887.