As temperatures begin to drop and households across the UK reach for the thermostat, heating experts are warning that one overlooked issue could leave homes cold – or even unsafe – this winter. According to engineers at home heating firm BOXT, thousands of Britons may be switching on their boilers for the first time in months without realising that hidden faults could be waiting to strike. From frozen pipes and seized valves to something as unexpected as birds nesting in boiler flues, engineers say a few quick checks now could prevent costly breakdowns later.
“Boiler breakdowns are one of the most common and expensive problems we see each winter,” said Adam Knight, the company’s lead engineer.
He added: “Many could be avoided with simple maintenance before the cold weather really sets in.”
Their data shows that nearly three in five households haven’t had their boiler serviced in the past year, and one in five admit they never service theirs at all. Homeowners in the East of England are the worst offenders, with 63% skipping an annual check, closely followed by the South East at 55%.
A replacement heat exchanger can cost up to £750, while a faulty circuit board can add another £450 to the bill – making prevention far cheaper than the cure.
It may sound surprising, but one of the biggest culprits for boiler failures at the start of winter comes from birds.
“Birds start nesting in spring, usually between March and August,” said Knight.
He added: “If they’ve made a home in or near your flue and it hasn’t been cleared afterwards, that blockage can stop your boiler working as soon as you fire it back up in autumn.”
The flue – the pipe that carries harmful gases safely outside – is one of the most important parts of any heating system. If it’s blocked, the boiler will usually shut itself off automatically as a safety precaution.
Before winter sets in, experts recommend doing a visual check from outside. Look for debris, rust or anything that looks out of place. If you notice unusual noises or error codes when turning your heating on, it could indicate a blocked or damaged flue.
“This is one of the simplest checks you can do, but also one of the most important,” Knight warns. “If something doesn’t look right, call a Gas Safe engineer immediately.”
After months of sitting idle, zone valves and thermostatic radiator valves (TRVs) can seize up, stopping heat from circulating properly. The result is rooms that stay icy cold even when the boiler appears to be running.
“Zone valves are essential for directing hot water around the house,” said Knight.
“We often see cases where the boiler is working perfectly, but some radiators remain cold because the valve is stuck. Catching that early saves frustration and unnecessary call-outs.”
Another frequent issue in winter is a frozen condensate pipe, which can shut the whole system down. If your boiler starts gurgling or displays a fault code, check the plastic pipe leading outside – it may just need thawing with warm (not boiling) water.
Additionally, low system pressure is one of the simplest but most overlooked faults. If the gauge drops below 1 bar, the boiler may stop working altogether.
“It’s a quick fix,” said Knight.
He added: “Top up the system gradually to 1–1.5 bar, and if pressure keeps falling, it could signal a leak.”
Meanwhile, wireless thermostats often lose battery power or connection after months of disuse. Replacing batteries and re-pairing the device with the boiler usually restores heating instantly – a simple check that can save a weekend without warmth.