Martin Lewis reveals we're all wasting money on this classic hot water mistake – but it's so easy to fix

This little boiler trick could save you precious pennies this winter

Martin Lewis portrait
(Image credit: Future PLC/Carolyn Barber)

Topping up a too-hot bath with cold water, or mixing hot and cold water running through a mixer tap to get the right temperature, might be common practice in many households, but Money Saving Expert Martin Lewis warns it could be a waste of your precious pennies. 

Saving energy at home is at the forefront of all our minds as we struggle through winter without cranking the heating up to keep the house warm in winter. However, Martin Lewis has pointed out that we could be wasting money on the simple mistake of not turning down the hot water temperature on the boiler. 

Martin Lewis hot water boiler mistake

In a clip from the Money Saving Expert's ITV show, he explains that this is a mistake even he is guilty of. 

'You run a hot bath, you run a hot shower and you add cold water to it. You’re paying to pump the heat up on your water and then it’s too hot – even though you’ve paid for it – and you’re now mixing it with cold water to reduce the temperature. It makes no sense,' he points out. 

'55 degrees is the recommendation on a combi boiler, it’s quite easy to do on a combi boiler. It’s slightly higher and more complex for other boilers. Just bring the temperature down, you don’t need it to be too hot.'

Bathroom conversion full of warmth and character. Vanity unit with white and green marble top

(Image credit: Future PLC/Simon Whitmore)

While the clip was originally aired in November 2022, the tip is still a good one and is supported by heating experts as an easy way to save money at home

Ben Gallizzi, energy expert at, says: 'Turning down the temperature of the hot water on your boiler can save energy and money.'

'A higher temperature will cost you more money because heaters use more energy to keep water hot. Additionally, there’s more heat loss at higher temperatures.'

However, there are a few safety factors he says you should consider first. 'Don’t lower the temperature too much, though. If the temperature is set below 60°C, it could allow harmful bacteria to grow in a hot water cylinder (if you have a conventional boiler).'

A hot water boiler stored in a tall wall kitchen cupboard unit, with shelves and wood worktop

(Image credit: Future PLC/Colin Poole)

Turn the hot water temperature down on a boiler

The amount of money you can save will depend on how much you need to turn your boiler's hot water temperature down. However, if you have found that the hot water coming out of the top is too hot for you to use, then you are wasting money.

Turning down the hot water temperature on a combi-boiler is relatively easy. It is usually indicated by a tap icon so you can lower it separately to your radiators. Other boilers might be more complicated to turn down the temperature, so check your appliance manual first. 

Rebecca Knight
Deputy Editor, Digital

Rebecca Knight has been the Deputy Editor on the Ideal Home Website since 2022. She graduated with a Masters degree in magazine journalism from City, University of London in 2018, before starting her journalism career as a staff writer on women's weekly magazines. She fell into the world of homes and interiors after joining the Ideal Home website team in 2019 as a Digital Writer. In 2020 she moved into position of Homes News Editor working across Homes & Gardens, LivingEtc, Real Homes, Gardeningetc and Ideal Home covering everything from the latest viral cleaning hack to the next big interior trend.