How Hot Should My Water Be?

The team at Custom Heat have been deeply moved and equally motivated by helping a wonderful Warwickshire family after one of their young sons, Jenson, suffered 93% burns to his body by climbing into a running bath. 

The water temperature was 70 degrees celsius, causing him significant, life-changing injuries. You can read more about their story, which touched the hearts of the community, here.

The temperature of the hot water from your boiler depends on the type of central heating system, how well it is working and how it is adjusted.

How to confirm the temperature of your hot water.

It isn’t sufficient to test hot water by running it onto your hand – as the base temperature of your hand will affect how your body perceives the temperature. It is much safer and more accurate to run your water for 20 seconds or so and then fill a large glass, like a pint glass. Dip a thermometer into the water to obtain the current temperature and make a note. 

So what temperature is considered safe?

Anything over 46 degrees, but ideally closer to 60 degrees should ensure that legionella bacteria – the cause of Legionnaires’ Disease – are destroyed. 

However, anything over 60 degrees will not only cause significant risk of scalding, particularly in children and vulnerable people, but also end up denting your wallet. 

How do I control the temperature?

First it depends on what type of boiler you have.  If you have a combi boiler, water goes directly from the boiler to the taps. 

A system boiler or conventional heat-only boiler heats water in a cylinder by pumping hot water through pipes around it. Water from the boiler circulates around the pipes over and over, but the water in the cylinder remains fresh. 

I have a combi boiler, how do I adjust the hot water temperature?

Most combi boilers have a manual way to control the temperature (either a knob or a slider) or if your boiler is newer, it could be a digital panel.  You should be able to adjust the heating and the water separately, so adjusting your hot water will not impact the efficacy of your heating.

As combi boilers heat water as it is needed, the results should be immediate and can be adjusted whenever needed.

I have a system or heat only boiler, how do I adjust the water temperature?

Adjusting the temperature on a system or heat only boiler is a little trickier, and results will not be immediate – but worth doing, as once it is set, it shouldn’t need adjusting very often. 

The temperature setting on the cylinder may be visible, but it may be behind a panel, so you may need to hunt for it. Some are digital, others are manual and may even need a screwdriver to adjust.  The control panel essentially tells the boiler when to push hot water around the cylinder, triggered by a minimum temperature in the cylinder – which means it may take a while longer to change the temperature. 

After a few hours have passed, or your hot tap has been run a few times, test again with the glass of water. 

How do I adjust the temperature from an immersion heater?

Immersion heaters have their own thermostats, and often require a cover being removed to access that thermostat, and you’ll probably need a screwdriver to get it off.  Once you have adjusted the thermostat, the effect will not be instant, and should be tested after a period of time.  If you want a faster result, you’ll need to run the hot tap to empty the tank before testing with a glass. 

I’ve tried all that, could it be a faulty boiler?

Yes, water that is running too hot could be caused by a mechanical or electrical failure.  If water flows too slowly over the heat exchanger, its temperature will rise too high.  It could also be that the thermostat needs replacing or repairing.  If you’ve tried manually adjusting the temperature on your boiler, and the water is still too hot, please call out an engineer.

If you’re unsure or need further guidance, please reach out to one of our friendly team, who will be able to support you. 

We want to make sure every one of you stays safe and is able to ensure the temperature of their water is correct, and are happy to support.

Our engineers will also check these parameters at every routine service, and anyone with a boiler care plan can book this annual service as part of their plan. Depending on your plan, you may be eligible for a free repair.