How Forgetting the Clocks Going Back Could Leave You in the Cold
Quick Answer: When the clocks go back in autumn, most programmable thermostats do not update automatically. If you don’t adjust your heating schedule, it will run an hour behind the new time — meaning your home may not be warm when you wake up or return from work. Checking and resetting your thermostat takes less than five minutes and can prevent both a cold morning and unnecessary energy waste.
It’s one of those things that slips through the net every year. The clocks go back on the last Sunday of October, most people remember to change the clock on the kitchen wall, and then the central heating thermostat sits quietly in the hallway running an hour out of sync for days — or weeks — before anyone notices.
The result is a heating system that fires at the wrong time, a house that is cold when it should be warm, and occasionally a heating schedule running longer than it needs to compensate for the missed timing. None of it is catastrophic, but it is avoidable, and understanding exactly what happens — and why different thermostats handle the clock change differently — makes it easy to stay ahead of the problem.
Key Entity Relationships
- The clocks going back refers to the end of British Summer Time (BST), which occurs on the last Sunday of October each year in the UK, when clocks revert to Greenwich Mean Time (GMT) by moving one hour back.
- A programmable thermostat is a heating control device that operates a central heating system according to a user-defined schedule of on and off times, and must be manually updated when the clocks change if it does not synchronise automatically.
- A smart thermostat is a wi-fi connected heating control device that can synchronise its time automatically via an internet connection, meaning it does not require manual adjustment when the clocks change.
- British Summer Time (BST) is the period from the last Sunday in March to the last Sunday in October during which UK clocks run one hour ahead of Greenwich Mean Time.
- Greenwich Mean Time (GMT) is the standard time reference used in the UK outside of British Summer Time, and the time to which all heating controls should be set after the clocks go back.
- A central heating boiler is the heat-generating appliance that responds to signals from the thermostat or programmer and fires to meet the schedule and temperature demands that have been programmed.
- A heating programmer is a time-based control unit that dictates when the central heating and hot water circuits switch on and off, and is distinct from the room thermostat that controls temperature.
- A room thermostat measures the ambient air temperature in a specific location and signals the boiler to fire or stop based on whether that temperature is above or below the set point, working in conjunction with the programmer’s time schedule.
- A smart thermostat’s machine learning capability allows it to build a profile of the household’s daily occupancy and temperature preferences, automatically adjusting the heating schedule over time to reduce energy waste.
- The Energy Saving Trust is a UK non-profit organisation that provides guidance on household energy efficiency, including recommendations on heating controls and thermostat use.
- A zone control system divides a property into separately controlled heating areas, each with its own thermostat and programmer, and each requiring independent time adjustment when the clocks change.
- Carbon monoxide is a colourless, odourless combustion byproduct that a poorly maintained boiler can produce at elevated levels, and annual servicing — which also ensures thermostat calibration — is the primary safeguard for UK households.
What Actually Happens When the Clocks Go Back
The UK moves from British Summer Time (BST) to Greenwich Mean Time (GMT) on the last Sunday of October. Clocks move back by one hour — so 2:00am becomes 1:00am — and the day gains an hour.
For most household devices, this is handled invisibly. Smartphones, laptops, and smart speakers update automatically via an internet or network time signal. But a standalone programmable thermostat or a boiler-mounted programmer has no such connection. It keeps running on the time it was last set to, which is now an hour ahead of the real time.
In practical terms, this means a heating schedule set to come on at 6:30am will now come on at what feels like 7:30am. If you are used to waking to a warm house, the first morning after the clocks go back can be a cold surprise. The same logic applies to evening programmes — a schedule set to heat the home from 5:00pm will now run from 6:00pm, which is fine in BST but means arriving home to a cold house in GMT.
The problem compounds itself if the discrepancy is left uncorrected for several days. The heating runs at the wrong time, the household compensates by manually overriding the system more than necessary, and the efficiency that a properly programmed thermostat provides is partly or wholly lost.
Which Thermostats Update Automatically — and Which Don’t
Not all heating controls behave the same way when the clocks change. Understanding which category your thermostat falls into determines whether you need to take any action.
| Thermostat Type | Auto-Updates for Clock Change? | Action Required |
|---|---|---|
| Smart thermostat (Nest, Hive, Honeywell Home) | Yes — syncs via internet connection | None — check app to confirm |
| Programmable room thermostat (no wi-fi) | No | Manual time reset required |
| Boiler-mounted programmer (e.g. Horstmann, Drayton) | No | Manual time reset required |
| Basic on/off thermostat (no timer function) | Not applicable — no schedule to update | None |
| Zoned smart control system | Yes — if internet connected | Check each zone in the app |
| Analogue dial thermostat | Not applicable | None |
If you are unsure which type you have, a quick check of whether the thermostat has a wi-fi or internet connectivity function is the simplest way to determine whether it will update automatically. If it does not connect to a network, assume the clock will need changing manually.
How to Update Your Thermostat When the Clocks Go Back
The process for resetting the time on a programmable thermostat varies between manufacturers and models, but the general approach is consistent. Most units have a clock or time button that initiates the adjustment mode, after which the hours and minutes can be changed using arrow or plus and minus buttons.
The ideal time to make this change is on the Sunday morning that the clocks go back, before the heating programme would next run. Resetting on Saturday evening — before you go to bed — is equally effective and means the heating will be correctly synchronised from the first overnight period in GMT.
What to Check Beyond Just the Time
Resetting the clock is the immediate priority, but the clock change is also a useful prompt for a broader review of your heating schedule. What was the right programme for late October BST may not be optimal for a November GMT programme in terms of when the house needs to be warm and for how long.
Consider whether the existing morning and evening on-times still reflect when people are actually in the house, whether the overnight setback temperature is appropriate for the colder nights ahead, and whether any rooms are being heated at times when they are consistently unoccupied. A few minutes spent reviewing the full programme is time well spent and can have a noticeable effect on heating costs through the winter months.
Smart Thermostats and the Clock Change
Smart thermostats — such as those in the Nest, Hive, and Honeywell Home ranges — handle the clock change automatically by synchronising their internal clock with an internet time server. The schedule stored in the device updates to reflect the new time without any input from the homeowner.
This is one of the more practical day-to-day advantages of a smart thermostat beyond its headline features. While automatic time synchronisation is a small thing, it sits alongside a broader set of functions — remote control via smartphone, occupancy sensing, and learning algorithms that adapt the schedule to actual usage patterns — that collectively make managing a heating system easier and less prone to the kind of oversight the clock change creates for conventional programmers.
Smart thermostats do vary in how they handle the adjustment period around the clock change, however. Some models may show a brief period of uncertainty as the schedule recalibrates to the new time reference. Checking the app on the morning of the clock change to confirm the schedule looks correct takes only a moment and provides reassurance that the system is running as expected.
What Smart Thermostats Can Do That Conventional Programmers Cannot
The clock change is a useful illustration of a broader truth about heating control. A conventional programmer running a fixed schedule requires active management to stay aligned with the household’s actual routine. A smart thermostat, by contrast, builds a dynamic picture of the household’s occupancy and temperature preferences over time, adjusting the programme automatically to minimise heating that serves no one.
The practical energy saving from this difference in approach depends on the household, but studies consistently show that well-managed smart thermostat installations reduce annual heating costs compared to a fixed schedule operated by a standard programmer. The Energy Saving Trust estimates that a correctly installed and configured smart thermostat can reduce heating energy use meaningfully for most UK households, with the exact saving depending on how the previous system was managed.
The Broader Energy Case for Getting Thermostat Settings Right
A heating programme that runs an hour behind the correct time is a minor inefficiency on its own. But it reflects a broader category of thermostat management that has a more significant cumulative effect on annual energy bills.
A thermostat set one degree higher than necessary can increase a household’s annual heating costs by a meaningful amount — figures cited by the Energy Saving Trust and similar bodies suggest each degree of unnecessary setpoint increase adds approximately three percent to heating bills. A programme that runs heating for an hour longer each day than the household actually requires compounds that effect further over the course of a winter.
Getting the thermostat settings right is therefore not just about the clock change. It is about ensuring that the heating schedule reflects how the household actually operates — when rooms are occupied, when they are not, and what temperature genuinely supports comfort without overshooting. The clock change is a useful annual prompt to revisit all of these questions at once.
Annual Boiler Servicing and Heating Control Accuracy
A thermostat that drifts in its calibration — reading a room temperature slightly above or below the actual temperature — will cause the boiler to fire at the wrong time or hold temperature longer than necessary. Over time, calibration drift in a room thermostat can have a more significant effect on energy use than a missed clock change, and it is something that an annual boiler service covers.
During a service, a Gas Safe registered engineer will test the thermostat’s accuracy, check that the programmer is functioning correctly, and verify that the system responds as expected to control inputs. This is also an opportunity to raise any questions about upgrading heating controls — if you are still running a conventional programmer, the engineer can advise on whether a smart thermostat would be straightforward to retrofit to your existing system.
Scheduling the annual service for September or early October — before the heating season begins in earnest — also means the system is in the best possible condition as the temperatures drop, and any issues with controls or boiler performance are identified before they become a problem rather than after.
You can find and verify Gas Safe registered engineers in your area at gassaferegister.co.uk.
Zone Controls and Properties with Multiple Programmers
In larger properties with zoned heating systems — where different areas of the house are controlled independently — the clock change requires attention to each zone separately. A property with one programmer for the ground floor and another for the upper floor, for example, needs both to be updated.
If any of the zone controllers have separate time displays, check each one individually rather than assuming they are all set the same. It is not uncommon for one zone to be updated and another to be missed, producing inconsistent heating behaviour that can take a day or two to trace back to a time discrepancy.
For properties with a home automation system that integrates heating control with other building functions, the manufacturer’s app or control interface will typically confirm whether the schedule has updated following the clock change. This is worth checking rather than assumed.
Can Forgetting to Change the Clocks Impact Boiler Frost Protection and Lead to Frozen Pipes?
Forgetting to change the clocks can indeed impact your boiler’s frost protection. As temperatures drop, an unmonitored boiler may fail to operate efficiently, leading to frozen pipes. To avoid this risk, always implement boiler frost prevention tips, ensuring your system runs smoothly even during the coldest nights.
FAQ
Do I need to change my thermostat when the clocks go back?
It depends on the type of thermostat you have. Smart thermostats that connect to the internet — such as Nest, Hive, or Honeywell Home models — synchronise their time automatically and require no manual adjustment. Conventional programmable thermostats and boiler-mounted programmers do not connect to a time server and must be updated manually when the clocks change. If your thermostat has no wi-fi connectivity, assume it needs resetting and check the display or manual for instructions.
What happens if I forget to change my thermostat when the clocks go back?
If a conventional programmable thermostat is not updated, it will run an hour behind the new time. The practical effect is that your heating programme fires one hour later than intended — so a 6:30am wake-up programme will now activate at 7:30am, and your home will be cold when you get up. The same applies to evening schedules. The error is easily corrected but can result in discomfort and slightly higher energy use if it goes unnoticed for several days.
When do the clocks go back in the UK?
The clocks go back on the last Sunday of October each year in the UK, marking the end of British Summer Time and the return to Greenwich Mean Time. At 2:00am, clocks move back to 1:00am, gaining an hour. In 2026, this falls on Sunday 25 October. The clocks go forward again on the last Sunday in March, at which point the same check should be applied in reverse to ensure heating programmes remain aligned with the new time.
Does a smart thermostat adjust automatically for the clocks going back?
Yes. Smart thermostats that connect to the internet synchronise their internal clock via a network time server and update automatically when the clocks change. Devices such as Nest, Hive, and Honeywell Home thermostats handle this without any input from the homeowner. It is still worth opening the app on the morning of the clock change to confirm the schedule looks correct, but in normal circumstances no manual adjustment is required.
How do I reset the time on my programmable thermostat?
The process varies between manufacturers and models, but most programmable thermostats have a clock, time, or set button that initiates a time adjustment mode. Once in this mode, you use arrow keys, plus and minus buttons, or a dial to move the hours and minutes to the correct time. Your thermostat’s user manual will include specific instructions for your model — if you no longer have the manual, the manufacturer’s website will typically provide a downloadable copy by searching the model number.
Can the wrong thermostat time increase my energy bills?
Yes, though the impact of a one-hour discrepancy is modest on its own. If the heating runs an hour later than intended each morning, the house is cold when it should be warm, and the boiler may need to run longer to reach temperature before the household leaves for the day. More significant energy waste tends to come from leaving an incorrect schedule in place for weeks, from a setpoint that is higher than necessary, or from a programme that runs heating for longer than the property is actually occupied.
Is the clock change a good time to review my heating programme?
Yes. The end of October clock change is one of the most practical moments to review your full heating schedule, not just update the time. Summer and early autumn usage patterns — when heating runs are shorter and setback temperatures higher — do not necessarily translate well into winter. Reviewing when the heating actually needs to be on, what temperature is genuinely required overnight, and whether any rooms are heated during periods of consistent non-occupancy can produce meaningful savings over the course of the heating season.
Should I book a boiler service before the clocks go back?
Scheduling an annual boiler service in September or early October — before the main heating season — is good practice for reasons beyond the clock change. The service gives a Gas Safe registered engineer the opportunity to check thermostat calibration, verify programmer function, and address any developing boiler issues before temperatures drop. A boiler that enters winter in peak condition is less likely to break down during a cold period, when engineer availability is lower and the wait for a repair is longer. Maintaining energy efficiency with your boiler not only reduces heating costs but also extends the lifespan of the appliance. Regular servicing helps identify any areas where improvements can be made, ensuring optimal performance throughout the winter months. Moreover, a well-functioning boiler operates more quietly and contributes to a comfortable home environment.
Conclusion
The clocks going back is a small but reliable annual disruption to central heating schedules, and one that is almost entirely avoidable with a few minutes of attention on the right Sunday morning. For households running a conventional programmable thermostat, updating the time when the clocks change is the immediate action. For those with smart thermostats, a quick check of the app on the same morning provides reassurance that the schedule has updated correctly.
The broader value of the clock change as a prompt is worth taking seriously. A heating schedule that accurately reflects when the house is occupied and what temperature is genuinely needed — rather than one set years ago and left to run regardless — makes a real difference to energy bills across a full winter.
If your boiler has not been serviced this year, scheduling it before the heating season is fully underway is the most effective single step you can take to ensure your heating system is ready for the months ahead. understanding back boiler function is essential for homeowners to maintain efficiency and safety in their heating systems. By familiarizing yourself with how the back boiler works, you can better identify any issues that may arise. Regular monitoring and maintenance can prevent costly repairs and ensure optimal performance during the colder months.
