Continuous flow and instantaneous hot water in the Sutherland Shire
Updated October 2026
Continuous flow hot water, also called instantaneous hot water, is the system that never runs out. There is no tank. A compact wall-mounted unit heats water on demand as it flows through, so the fourth shower of the morning is as hot as the first. Shire Hot Water connects you with licensed plumbers and gas fitters across the Sutherland Shire who install, replace and repair continuous flow systems from brands like Rinnai, Bosch, Rheem and Thermann.
We are a referral service, not a plumbing business. The licensed hot water plumbers we work with handle the plumbing, with licensed gas fitters on gas units and licensed electricians on hard-wired electric units, as NSW requires.
How continuous flow works
When you open a hot tap, the unit senses the flow and fires a gas burner (or, less commonly, electric elements) around a heat exchanger. Water heats as it passes through and stops heating the moment you close the tap. No tank means no stored water going cold overnight, no standing heat loss, and no cylinder to corrode and flood the garage. Most units deliver water at a preset temperature, and many support bathroom controllers that let you dial in an exact temperature at the tap.
Why Shire households choose it
- Endless hot water. Sized correctly, it keeps up with back-to-back showers, a bath and the dishwasher.
- Space. The unit is the size of a small suitcase on an external wall. For tight side passages and apartment balconies common in Caringbah and Cronulla, that matters.
- Lifespan. With no tank to corrode, continuous flow units commonly last 15 to 20 years with occasional servicing, versus 8 to 12 for a storage tank.
- Efficiency. You only heat the water you use. For gas households, running costs are typically lower than gas storage.
The trade-off is that gas units need adequate gas supply. Older or undersized gas lines sometimes need upgrading to feed a large unit, and mains gas availability varies street by street in the Shire, so the plumber checks your meter and line before quoting. Our gas hot water page covers gas supply in more detail.
Sizing: litres per minute, not litres
Continuous flow units are rated by flow, not capacity. As a guide, a 20L/min unit suits most two-bathroom Shire homes, while 26L/min suits larger households likely to run two showers and a tap at once. Undersizing is the common mistake: the unit still works, but flow drops when multiple outlets run. Tell the plumber how many bathrooms you have and how your household actually uses hot water, and they will size it properly.
Repair or replace
Continuous flow units display error codes when something fails, which makes diagnosis fast. Igniters, sensors, valves and fans are all repairable, and on a unit under ten years old, repair is usually the right call. If the heat exchanger has failed on an older unit, replacement normally makes more sense. Swapping an old continuous flow unit for a new one on the same wall is one of the quickest hot water jobs there is, often done in a couple of hours.
Coastal placement matters here too. Externally mounted units near the water at Cronulla, Kurnell and Bundeena wear faster in salt air, so position and servicing intervals deserve attention in those streets.
Cost and licensing
Installed pricing varies with unit size, flueing and whether the gas line needs upgrading, with gas systems as a category typically running about $1,200 to $3,500 installed in Australia. A like-for-like continuous flow swap sits comfortably inside that range, while converting from a storage tank costs more because pipework and gas supply change.
In NSW, the plumbing must be done by a licensed plumber and gas connections by a licensed gas fitter. Hard-wired electric continuous flow units need a licensed electrician. Every tradesperson we refer holds the licences their part of the job requires.
Get a fast quote for continuous flow hot water from a licensed Shire plumber.
Frequently asked questions
Is continuous flow hot water really instant?
The unit heats instantly, but the hot water still has to travel from the unit to your tap, so there is a short delay, the same as with a tank. Units mounted close to the main bathroom, or paired with a recirculation setup, cut the wait.
What size continuous flow unit do I need?
For most two-bathroom homes, 20L/min. For larger households running multiple showers at once, 26L/min. Smaller 16L/min units suit one-bathroom homes and units. The plumber sizes it from your bathroom count and usage, which is worth getting right, as undersized units frustrate everyone every morning.
Can I replace my storage tank with continuous flow?
Usually yes, and it frees up the space the tank occupied. The job involves new pipework to the wall position, flueing and often a gas line check, so it costs more than a like-for-like swap and typically takes most of a day.
My continuous flow unit is showing an error code. What do I do?
Note the code, try turning the unit off and on at the isolation switch, and if the code returns, book a plumber. Codes map to specific faults, ignition, sensors, flow, so the plumber often arrives knowing what part is likely needed.