Hot water arrives slowly because the pipe between the heater and the tap is full of cold, standing water that must be pushed out first. Pipe length, your system type, the heating cycle, and the condition of the heating element all add to that wait.
If your hot water takes a while to show up, that is completely normal in most homes. But at some point, a slow tap stops being about physics and starts being about a system on its way out.
Between your hot water unit and your tap sits a length of pipe, and whatever water is sitting in it right now is cold. It has cooled to room temperature, or close to it, because nothing has been flowing through it. When you turn the tap on, that cold water has to come out before the hot water behind it can arrive.
This is the whole story behind most hot water delay. It is not a fault or a sign your system is working badly. It is simply the volume of standing water between the heater and the tap being physically displaced before hot water reaches the outlet.
Two things determine how much cold water sits there: the length of the pipe run and its width. Both are fixed by how the house was plumbed, which is why some taps in a house are instant, and others take a while, even off the same hot water system.
Australian residential plumbing typically runs on 20mm copper pipe (DN20 under AS 1432, the local copper tube standard). A 10-metre run of that pipe holds roughly 2.3 litres of standing cold water.
At a standard basin or shower flow rate of 6 to 9 litres a minute, that 2.3 litres takes about 15 to 23 seconds to clear before hot water shows up. Double the pipe length, and you roughly double that wait, because the volume of water in the pipe scales directly with its length.
Diameter is also more than most people expect, because pipe volume increases with the square of the radius, not in a straight line. A pipe that is slightly wider holds noticeably more water, not just a little more. This is why an ensuite at the far end of the house, fed by a longer or wider run, can take twice as long as a bathroom near the kitchen.
You can’t eyeball any of this accurately from outside the wall. If you want to know exactly how much pipe is between your heater and a given tap, that is a job for whoever plumbed the house, or a licensed plumber doing an inspection.
Both storage and continuous flow systems have to deal with the same pipe-run delay described above. What differs is whether anything extra is added on top of it.
| Electric or gas storage | Continuous flow (instantaneous) | |
| Water source | Pre-heated water already sitting in a tank | Heated on demand as it passes through the unit |
| Extra delay before pipe-run displacement | None. Tank water is ready to go the moment the tap opens | A short start-up period while the burner ignites and the heat exchanger comes up to temperature |
| Typical cause of a “slow” tap | Pipe-run displacement only | Pipe-run displacement, plus start-up lag |
A storage system has hot water sitting ready in the tank, so the only delay is the pipe run. A continuous flow unit heats water as it passes through, and Rinnai, one of the most widely installed continuous flow brands in Australia, describes this start-up period simply as the unit taking “a few seconds” to begin heating once a tap is opened. That start-up period then adds to any pipe-run delay already in place.
In practice, this means continuous flow is not automatically the faster option at the tap. It is more efficient and won’t run out of hot water the way a tank can, but waiting at a distant tap can feel similar to, or slightly longer than, a storage system.
If you have a continuous flow system, you may have noticed that you turn the hot tap off for a few seconds, then turn it back on, and a burst of cold water comes through before the hot returns. That is the cold water sandwich effect, and it is specific to continuous flow units.
But why does it happen? Well, the burner only fires while water is flowing. The moment you pause the tap, even briefly, the burner shuts off. The water that is already sitting in the pipe between the unit and the tap starts cooling straight away. When you turn the tap back on, that now-cooled water arrives first, before the burner has re-ignited and heated a fresh supply behind it.
It can seem like the system just failed, but it’s really the unit doing exactly what it is designed to do. Storage systems don’t have this issue, because there is no burner to shut off. The tank just keeps its water hot regardless of whether a tap is open.
Off-peak systems heat overnight on a scheduled window set by your electricity distributor, and mornings are when a slow tap is most noticeable if you’re on one of these tariffs.
| State | Network | Typical off-peak window |
| NSW | Ausgrid controlled load | ~10pm–7am |
| VIC | Citipower | ~11pm–7am |
| QLD | Energex tariff 33 | Varies — check your bill |
Two things can line up badly on a winter morning. First, if your first shower happens right at the edge of that heating window, the tank might not have fully finished its overnight cycle yet. Second, overnight the pipe has had hours to cool to ambient temperature, so it has more heat loss to make up before hot water reaches the tap, on top of the usual pipe-run delay.
Neither of these is a fault. It is the combination of tariff timing and a cold pipe after a long overnight idle period. If your morning wait is dramatically longer than at any other time of day, or has been getting worse specifically at that time, mention it to a technician, but a few extra seconds in winter is expected behaviour for an off-peak system.
A note on off-peak windows: these vary by state, network, and retailer, and they’re reviewed periodically. Check your own electricity bill or your distributor’s website for the exact hours that apply to your property.
Storage systems typically have two elements: an upper element and a lower element. The two fail differently, and knowing which one is going is a useful diagnostic on its own.
The pattern that is easy to miss is the one in between. Before an element fails completely, it often degrades gradually. You might notice your hot water duration shortening week by week, or the peak temperature dropping slightly each time, before the system eventually gives you no hot water at all. That changing pattern, not the delay itself, is the signal worth paying attention to. A system that is simply slow because of pipe length looks the same every single time. A system with a failing element gets a little worse each week.
Yes. An uninsulated pipe loses heat to the surrounding air whenever water sits idle, which is most of the time between draws. In winter, or in an unheated roof space where many Australian homes route their hot water pipework, that heat loss is worse because the temperature difference between the pipe and its surroundings is bigger.
The practical effect is that the water sitting in the pipe is colder than it would be on a mild day, so slightly more of it needs to be displaced before what arrives at the tap actually feels hot. It is the same pipe-run mechanism from earlier in this article, just made a bit worse by ambient temperature.
Pipe insulation is one of the cheaper fixes available and is worth considering on any exposed or roof-space run, particularly in southern states where roof cavities can get genuinely cold overnight in winter.
Ordinary pipe-run delay looks the same every time you turn on the tap. It is consistent, predictable, and does not get worse. Replacement is a different conversation, and it is worth having one if you are seeing any of the following:
Any one of those on its own is worth a look. Several together, especially on an older system, usually means an element or thermostat is on the way out rather than the pipework being the culprit. At that point, repair costs start to compete directly with the cost of a straightforward replacement, and a licensed technician can tell you quickly which side of that line your system sits on.
There are five practical options, roughly in order of cost and disruption.
If you are not sure which of these applies to your situation, a same-day assessment from a licensed technician can sort it out quickly, rather than guessing and paying for the wrong fix. If you need assistance, speak with our team at Same Day Hot Water.