If you find yourself with no hot water but your heating still works, you'd be forgiven for thinking it makes no sense. We'd think the same too, which is why we've asked heating experts to explain why this problem occurs.
And, with a study revealing 1 in 5 of us faced heating issues this time last year*, it's probably important you arm yourself with this particular knowledge now, in case you find yourself in a similar situation before the winter ends.
From the simple steps you can take to fix the problem yourself to the faults where only a heating engineer will do, here's why you can sometimes have no hot water but your heating system still works.
4 steps before you call in a professional
The good news is, before you race to find a heating engineer to fix the problem, there are a number of checks you can perform yourself. While they may not always fix the problem, there's a chance they could – potentially saving you time and money in the process.
1. Check the pressure
"Start by checking the boiler pressure; most systems should sit between 1 and 2 bar. If the pressure is too low, the boiler may struggle to deliver hot water," explains Adam Knight, a lead engineer at BOXT. "Many boilers can be safely repressurised by following the manufacturer’s guidance, but you should never force any valves or overfill the system," he warns.
2. Look at the thermostat settings
“Next, make sure you also check the hot water thermostat," says John Klee, heating and technology expert at Best Heating. "It may sound obvious, but the temperature control can easily be turned down accidentally while adjusting the heating settings. Ensure the thermostat is set correctly and that the settings on the control panel match those on the boiler itself," he adds.
"Make sure the timer is set correctly, and if the controls use batteries, replacing them is a simple step that is also often overlooked," adds Adam Knight.
3. Check all visible pipework
"Your next step is to take a look at your radiators and any visible pipework," says Adam Knight. "Cold spots on radiators can be a sign of trapped air, which can usually be released by radiator bleeding. It’s also worth checking around the boiler for any visible leaks. But, if you do see water, don’t open the boiler casing or try to fix it yourself," he warns.
"In colder weather, also look for any signs of frozen pipes," says John Klee, noting that, "it’s also worth checking with neighbours to see if their supply is affected, as this can rule out a wider water service issue in your area."
Try this easy-to-use radiator bleed key with integrated reservoir if your radiator needs bleeding to help balance the pressure that could be blocking your hot water supply
4. Try a boiler reset
"Finally, try the simplest step which is to reset the boiler," says John Klee. "Switch it off, wait at least 30 minutes, then turn it back on to allow the internal components to fully reset.
"If your system has a diverter valve on a separate circuit, switch this off and on as well. This can often resolve minor faults and restore normal hot water flow."
Adam Knight is a lead engineer at heating and cooling experts, BOXT. Adam brings over 17 years of industry experience, including 14 years at British Gas specialising in auditing, gas qualifications, and incident investigations, and now leads BOXT’s Tech Survey Team with specialist training in air conditioning and heat pump systems.
John is a heating technology expert at Best Heating, where for over nine years he has dedicated himself to demystifying home heating for our customers. He specialises in creating clear, data-driven guides and how-to articles by collaborating directly with Bestheating's team of certified experts and product engineers.
When you'll need to call in a professional heating engineer
Tried all four steps? Then it's likely time to accept you need professional help, particularly given the advice from Adam Knight who says, "what you should never do is remove the boiler cover, interfere with internal components, or try to ‘reset’ the system repeatedly if it keeps failing.
If these basic checks don’t help, it’s safest to stop and call a Gas Safe registered engineer.”
So what could be the cause of the fact you have no hot water but your heating still works? Before you start searching and worrying about new boiler costs, our experts say the positive news is that you might not need to replace your boiler.
“When heating works but hot water doesn’t, the problem is often down to a specific component rather than the whole boiler," advises Adam Knight.
"In combi boilers, a faulty diverter valve is one of the most common causes. This valve directs heat either to the radiators or to your taps. If it sticks, the boiler may heat the home but fail to produce hot water for taps or showers. This is a common repair and does not usually require a new boiler."
"Although repairing or replacing a diverter valve is a relatively straightforward task for a qualified heating engineer," adds John Keel, "the component itself can be difficult to access. It should never be removed or tampered with by anyone who isn’t trained and certified to work on boilers.
"A Gas Safe-registered professional will be able to diagnose whether the fault lies with the diverter valve or within the boiler itself and advise whether repair or replacement is the most efficient long-term solution."
It can also keep you up to date with any boiler maintenance, he adds, as "an engineer can also confirm that your heating and hot water systems are otherwise functioning safely and efficiently."
Other potential causes
But, if the problem isn't a faulty diverter valve, there are also other situations when a professional is required.
"Another common issue can be a failed thermistor or temperature sensor; these components tell the boiler when to heat the water," explains Adam Knight. "If they stop working, the boiler may not respond to hot water demand, even though the heating is still running.
"Problems with the heat exchanger or pressure-related faults can cause similar symptoms and, in many cases, are repairable," he adds.
Worried you still might need a new boiler if you have not hot water but still have heating? Try not to worry until an engineer has found the problem is Adam's advice.
"Replacement is usually only considered when a boiler is older, typically ten to twelve years, or when several components start failing at the same time. If repair costs are mounting, parts are difficult to source, or the boiler has become inefficient and unreliable, replacing it can often be the more cost-effective and dependable option. An annual boiler service should help identify any potential issues," he says.
"But, in most cases, heating without hot water is fixable," he confirms. "The age, condition, and repair history of the boiler are what ultimately determine whether repair or replacement makes sense.”
Both your heating and hot water playing up? Find out what other boiler problems could be causing your system to act up. Plus, once any issues are fixed, make sure your boiler flow temperature isn't set too high to help you save your energy bills in winter.
And, if you do find out you're in need of a new boiler, find out if how Beth Murton, Homebuilding & Renovating's editor got on when she tried the BOXT next-day installation service.
*A study of 2,028 UK adults commissioned by BOXT, carried out by Sago UK between 5th and 7th March 2025 revealed one in five Brits (18%) have faced heating and hot water problems in February 2025.
