Why September is the Most Expensive Month for Your Boiler
August 27, 2025
As households prepare to switch their boilers back on after summer, heating engineers are warning that September is often the most expensive month of the year for boiler breakdowns, repairs, and inefficiency.
Rob Jones, heating engineer at UK Radiators, explains:
“After months of being idle, boilers are suddenly put under pressure when temperatures drop in September. It’s the equivalent of asking someone to run a marathon after sitting on the sofa all summer – parts fail, pressure drops, and efficiency suffers. That’s why we see a huge spike in callouts every September.”
The Hidden Costs of the September Switch-On
- Pressure Loss – Idle boilers often lose pressure slowly over summer. When switched back on, this can cause heating not to fire properly.
- Sludge Build-Up – With water sitting still in the system, rust and debris settle, leading to cold spots and higher bills.
- Stuck Valves – Radiator valves and pumps can seize up when unused, forcing costly repairs once the heating is needed again.
- Air Locks – Radiators switched on after months off often need bleeding; without it, boilers work harder and waste energy.
- Undetected Leaks – Small leaks go unnoticed over summer but become expensive emergencies as the system is pressurised again.
Why September Bills Spike
According to UK Radiators, homeowners often use more energy in September than they realise:
- Days are warm, but evenings are cool, leading to boilers being switched on and off repeatedly (which uses more energy than consistent running).
- Families are back from summer holidays and schools reopen, meaning more showers, laundry, and hot water demand.
- Old habits — like turning unused radiators fully off — increase the risk of condensation, damp, and higher repair costs later.
Engineer’s Advice to Avoid the “September Surge”
Rob Jones advises:
- Check boiler pressure now – top it up if it’s dropped below 1 bar.
- Bleed radiators before switching on to avoid airlocks.
- Run your heating for 15 minutes once a month in summer to prevent valves and pumps seizing up.
- Book a service before the cold snap – engineers are busiest in September, so waiting can mean longer waits and higher emergency fees.
Rob Jones adds:
“The cost of a simple service in August or early September is far less than the repair bill we see when boilers give up later in the month. A little prep saves a lot of money.”
You May Also Enjoy
Rental price and average salary tracker – March 2026
Rents Plateau, But UK Market Tells Regional Story Significant comparisons include across Scotland where average agreed rents rose to £1,123, representing a 4.95% increase month and month across the nation. Northern Ireland saw the second largest average monthly rents rise, bringing an increase of 3.99% to an average agreed price of £887 compared to £853…
Read More 
Breaking Property News 9/4/26
Daily bite-sized proptech and property news in partnership with Proptech-X. Why Rightmove is making all the wrong moves In a world reshaped by AI, incumbency is no longer protection. It is exposure. Thought Leadership By Andrew Stanton, CEO Proptech-PR Rightmove has long been the unassailable giant of UK property portals—a category-defining platform that, for years, operated…
Read More 
Six property firms expelled from redress scheme
Six property businesses have been expelled from The Property Ombudsman after failing to pay compensation awards. The expulsions followed a review by the scheme’s independent Compliance Committee, which agreed that each firm should be removed for breaching their membership obligations by not complying with Ombudsman decisions. The Property Ombudsman, which provides impartial dispute resolution for…
Read More 
Best garden renovations to increase property value this spring
With spring fast approaching and warmer weather finally in sight, now is the perfect time to step outside and give your garden the well-deserved TLC and refresh it needs after such a wet and dreary start to the year. Whether it’s refreshing planting beds, updating patio areas or rethinking your layout, investing time into your…
Read More 
Prime London property market stays firm
The latest Prime London Demand Index by London lettings and estate agent, Benham and Reeves, reveals that, despite broad economic uncertainty, buyer demand across London’s most prestigious neighbourhoods avoided a decline during the first quarter of 2026, with the likes of Chelsea, Battersea, Highgate, and Belgravia seeing quarterly demand increases of above 5%. The Prime…
Read More 
More first-time buyers enter the market in 2026
The latest research by Yopa has revealed that first-time buyer demand has strengthened during the first quarter of 2026, despite the supply of homes offering the benefit of a buying scheme remaining limited. Yopa analysed first-time buyer demand based on the proportion of homes listed under buying schemes* that have already sold subject to contract…
Read More