A continuous flow system heats water only while it is being drawn. Open a tap, the unit senses flow, fires, and heats the water on its way past. Close the tap and it stops. There is no tank, so there is no reservoir to empty and no stored water losing heat while nobody is home.
It is a common choice on Sunshine Coast properties where space is tight or a tank has nowhere sensible to go.
The trade is that it works to a rate rather than a volume. It can heat so much water per minute, and the sizing question is not how much you use in a day but how much you might draw at the same moment.
Flow rate: the number that actually matters
A continuous flow unit is rated by how many litres per minute it can raise by a given temperature. That rating assumes an incoming water temperature, and incoming water is cooler in winter, so the same unit delivers less on a cold morning than on a warm afternoon.
The practical sizing question is simultaneous outlets. One shower is straightforward. Two showers at once, or a shower plus the kitchen sink, is where an undersized unit shows itself.
The symptom is specific and worth recognising: not cold water, but the temperature sagging at one outlet when another opens. If that describes your existing system, it is undersized rather than broken.
Minimum activation flow
The unit needs a certain amount of water moving before it will fire. Below that threshold you get cold water, because the burner has not engaged.
This catches people with very low-flow fixtures, or with a tap opened only slightly. It is a design characteristic rather than a fault, but it is the sort of thing that generates a service call because nobody mentioned it at installation.
The cold-water sandwich, and the wait
Water sitting in the pipe between the unit and the tap is at room temperature. When you open the tap, that has to come through before the heated water arrives, so there is a delay proportional to the length of the run.
On a compact house it is barely noticeable. On a long run to a distant bathroom it is genuinely annoying, and it is one reason unit placement is worth thinking about rather than defaulting to where the old system was.
You can also get a brief cold slug mid-use if the unit cycles off and on, typically when flow drops near the activation threshold.
Gas, electric, and what the property can supply
Most continuous flow units on the Sunshine Coast are gas. Electric continuous flow exists but draws a substantial current for the heating it does, and the switchboard and supply have to carry it, which limits where it is practical.
For gas, the supply question is the one that catches people: a continuous flow unit demands considerably more gas while running than a small storage heater, and the existing line and meter were sized for whatever was there before.
Establishing that before the quote is agreed is the difference between a smooth installation and an unwelcome conversation on the day.
It wins where space is tight, since there is no cylinder. It wins where demand is spread rather than concentrated, and where nobody wants to think about running out. It wins where standby loss from a tank is an irritation.
It is less convincing where several outlets genuinely run at once and the flow rate would have to be large, where the gas supply cannot carry it without an upgrade, or where the household would rather have a reservoir than a rate.
As always, it is a property question rather than a technology question.
Continuous flow units are controller-driven, so faults usually announce themselves as an error code. Those codes are manufacturer-specific and worth sending us before a visit: some indicate a reset, others a part.
Ignition components, flow sensors and heat exchangers are the usual suspects. Scale can build up in the heat exchanger over time depending on water quality.
Because there is no tank, a fault removes your hot water immediately rather than after a reservoir empties, which is worth knowing when deciding how urgently to deal with an intermittent problem.
It will not run out of volume, which is the usual promise and it is true. What it can do is fall short on rate: it heats a certain amount of water per minute, and beyond that the temperature drops. So the failure mode is not a cold shower after twenty minutes, it is a cooler shower the moment someone opens the kitchen tap.
How is a continuous flow unit sized?
By flow rate rather than capacity. The question is how many outlets might run at once and what the unit can deliver at your desired temperature. Incoming water temperature matters too, since the unit is raising water from whatever it arrives at, and that is cooler in winter.
Why does the water go cold briefly then hot again?
Often the slug of water sitting in the pipe between the unit and the tap, which is at room temperature and has to be pushed through before the heated water arrives. On a long run to a distant bathroom that is a noticeable wait. It can also be the unit cycling if the flow is near its activation threshold.
Why will it not fire for a small trickle?
Continuous flow units need a minimum flow rate to activate the burner, as a safety and control measure. A tap opened barely, or a very low-flow fixture, can sit under that threshold and get cold water. It is a characteristic of the technology rather than a fault, though it surprises people.
Do I still need a tank?
No, and that is one of the main attractions: a wall-mounted unit and no cylinder taking up space or losing heat while you are at work. It also means there is no reservoir, so a fault takes your hot water away immediately rather than after the tank empties.
Can I add a second unit later?
In some configurations yes, and it is a common answer for a household or a business that has outgrown a single unit. It needs the gas or electrical supply to carry both, which is worth checking before assuming it is an easy future upgrade.
RCM works across Sunshine Coast and the hinterland. See the full Sunshine Coast service area for where we work regularly and where we travel on different terms.
