Too Hot, Not Hot Enough: How Your Water Temperature Is Actually Controlled

Your tank’s stored temperature is legally higher than the temperature the taps it feeds are legally allowed to deliver, which is why most of the temperature mysteries in Australian homes are solved: why the temperature of the taps in the kitchen is sometimes higher than the shower, why pressing up on the thermostat does nothing, why you have a scalding hot tap in the kitchen and a lukewarm one in the shower, and why one small valve near your tank is quietly one of the most important safety devices you own. You’ll learn how your water temperature is actually controlled, and how to read the temperature when the control malfunctions in either direction.

The First Number: 60°c, Because Of What Lives In Warm Water

Water in storage tanks should be kept at 60°C, and the motive is biological. Legionella bacteria are the cause of Legionnaires’ disease and grow much more happily in warm, stagnant water, and only die reliably at high temperatures. The bacteria cannot establish at 60 degrees, so 60 degrees isn’t a tip-of-the-hat recommendation, it’s a requirement for all stored hot water. Which is why “just turn the tank down to save energy” can only go so far, and why a tank that’s actually storing not-hot water (as opposed to delivering hot water) is a problem that’s worth addressing sooner rather than later, because it’s also a health issue. The obvious drawback of the 60-degree rule is that water at 60°C is hot enough to scorch one’s skin, hence the second number.

The Second Number: 50°c, Because Of Skin

The scald arithmetic is sobering, and to be known exactly, because it is so non-intuitive. Water burns a child in just a second, quicker than a parent two steps away can make it, at 60°C. Reduce the temperature to 50°C and that exposure becomes a moment, a margin for reflexes, supervision and common sense to operate effectively, instead of minutes. Those huge safety margins across a relatively small temperature difference are why NSW legislates for hot water to be limited to 50°C in bathrooms, where children and elderly people come into contact with water, and why sensitive areas, such as aged care and early childhood centres, keep it even lower at 45°C. Together the two numbers constitute the whole job of the system: storing at 60 for the bacteria, releasing at 50 for the skin, and handling the difference between the two.

The Manager In The Middle: Your Tempering Valve

A simple brass gadget on the pipework not far from your system, the tempering valve balances out the temperature difference between hot and cold water by infusing cold water into the hot water stream until it reaches the safe temperature. It is always there, silently running on all the hot taps you use, and it has two characteristics that every owner must be aware of. First, it’s a wear item: parts wear out and scale with the years, and many of us don’t bother to change it, nor do we know that it exists. Second, it is its failure direction that will specify your complaint. If it fails towards cold, as it usually does, it over-blends, which slows down delivery while the tank behind it is just hot: the “system running, taps disappointing” predicament. If it fails towards hot, rarer, and truly urgent, it under-blends, dumping scald-prone water into the rooms the law safeguards. Homes desiring maximum protection should upgrade to the more precise, tighter-tolerance sister of the tempering valve, the thermostatic mixing valve, which is used in healthcare and care settings.

Why The Kitchen Runs Hotter Than The Bathroom (And Other Legal Mysteries)

The detail that settles a thousand household arguments: the 50-degree cap only goes on bathrooms and personal-hygiene outlets, and not necessarily on every tap in the house. Hot water used for washing dishes and other chores in kitchens and laundries, or the laundry of small children who are not taking a bath, is usually connected outside the tempered circuit, particularly in older installations. So if a kitchen tap is a bit warmer than the ensuite, it’s not a fault, it’s doing what it’s designed to do, and it’s the most useful diagnostic in this article. If the kitchen runs hot but the bathroom is lukewarm, the tank proves itself by the untempered line and the fault is the tempering valve; and if the bathroom runs above 50°C, it points at a failed valve, or at an older house which had no valve at all, and it’s worthwhile to bring it up to standard when doing hot water work.

Reading Your Own System: Both Complaints, Diagnosed

Not hot enough: do the comparison diagnostics above (kitchen versus bathroom, temperature versus duration) and don’t bother cranking the storage thermostat, the delivery limit is imposed by the tempering valve anyhow, so a hotter tank is mostly going to waste energy and put stress on the tank while the lukewarm taps remain lukewarm. If the valve is convicted, the valve needs to be replaced; if the entire system under-delivers, then the thermostat, element and sediment chapters apply.

Too hot: set the location. If the bathroom outlets are measurably above 50°C, it means there is a failed or missing tempering valve, treat it as such and act accordingly, according to the severity of the situation and depending on which household members live there. The problem is more likely to be the layout, and less likely to be a fault, if it’s a hot kitchen. Everything scalding, or a high-limit cutout running, a sounding tank and a stressed TPR valve, means the thermostat is running away, a real safety fault where the high-limit cutout and the TPR valve are getting their job done, and a call the same day is expected. The low-cost thermometer under a flowing hot tap converts all of this into numbers, sixty seconds’ worth with any phone, accurate to the numbers.

Who’s Allowed To Adjust What

The adjustment map is important, due to the fact that this system is located in the region of 240 volts, stored heat and child safety. Yours: measure the temperature of the water, loosen the TPR valve every six months, and, always, check the water temperature for babies and small children, either with a thermometer or by elbow (for little ones, it’s around 37-38°C, a different number from anything above). The plumber’s: adjusting the thermostat on an electric system (behind covers, sharing space with mains wiring); installing, replacing and adjusting tempering valves; and upgrading legacy untempered systems to meet the standard. The way it’s put, it’s okay to measure everything and change nothing wet or wired: a division of labour worth respecting, given what the two numbers are designed to protect against.

Questions We’re Often Asked

Can the tempering valve be turned up so my showers run hotter?

There’s a little room to play with within legal parameters that a plumber can work on, but the 50° bathroom cap is not something that’s up for negotiation, nor is any attempt to bypass or over-range the valve legal or safe. And a true confession: 50°C is pretty hot (most showers are in the low forties), so a weak hot shower is not a cap set too low, it’s a valve leaking towards cold, or a system that is under-delivering, both of which can be fixed.

Do solar and heat pump systems have tempering valves too?

Yes, the rules apply to hot water stored in the tank, not to the way in which it is heated; solar systems are probably most in need of tempering, because a good collector day can get storage well over 60°C, leaving the blend-down to 50°C the sole means of separating the roof from the bathroom. Same valve, same service life, same failure signatures.

We’re renting and the hot water comes out scalding. Whose problem?

The landlord’s, and the delivery of safe hot water, promptly: bathroom hot water above 50°C indicates the property has either a failed tempering valve or a missing one, which requires professional attention. If you have a thermometer, take a reading, jump into writing a report, while keeping children away from unmixed hot taps, and treat the scalding rental bathroom as a very urgent maintenance task.

Is 45°C at home a good idea if we have small kids?

This is a strong dialogue to have with your plumber; the childcare-setting standard was created since child care centres have more stringent delivery temperatures and young skin burns quicker. The compromises are pragmatic (less hot water used in each shower, and colder maximum bath water temperatures) and the same valve family of hardware. For many families, the larger rewards are the easy ones: guaranteed 50°C delivery, pressure-balanced shower mixers, and the unbreakable elbow-test habit.

The Bottom Line

The hot water temperature is not a single and fixed value, it is a difference between two legal water temperatures, with a hardworking, mortal little valve responsible for the difference. The scalding bathrooms are demanding that valve urgently, and the lukewarm-tap complaints are accusing it of slacking. Both of the classic household temperature complaints are the same routine, a very important fix: learn the two numbers, measure before adjusting, keep the valve on its five-to-eight-year schedule.

Compiled by the Premium Sydney Plumbers team, licensed plumbers servicing hot water systems of all kinds throughout Sydney, with same-day service available where possible. Help is a call away on 1300 026 452, any hour of the day, if your hot water service isn’t working.