A generator that hasn’t been serviced is a gamble, and winter is when the odds turn against you. The last few winters have shown just how long the grid can stay down across the UK and Ireland, often for days rather than hours. Generator servicing for winter is the simplest way to make sure your backup power starts first time when the lights go out.
Winter power cuts in the UK and Ireland: the numbers
Three winter storms in four years have each left hundreds of thousands of homes, farms and businesses without mains power.
| Storm | When | Peak customers off supply | How long the worst-hit waited |
|---|---|---|---|
Storm Éowyn | January 2025 | 768,000 in the Republic of Ireland plus around 283,000 in Northern Ireland — over one million across the island | Up to 10 days; NIE Networks warned some properties wouldn’t be reconnected until 3 February |
Storm Darragh | December 2024 | Around 395,000 in the Republic of Ireland; 177,000 homes across England, Scotland and Wales | Around seven days for full restoration in Ireland |
Storm Arwen | November 2021 | Nearly 1 million homes in Great Britain | Nearly 4,000 homes off for over a week; some for more than 10 days |
A few figures stand out for anyone relying on backup power:
- Days, not hours. During Storm Arwen, 82% of customers were back on within 24 hours — but the remainder faced waits of up to a week or more in freezing conditions (Ofgem).
- Knock-on outages. Storm Éowyn also knocked out water treatment plants and broadband for around 160,000 premises (RTÉ).
- Restoration estimates aren’t guaranteed. Ofgem found 28% of Arwen customers were told they’d be back on within a day when that wasn’t accurate (STV).
- Storms are getting worse. Éowyn brought the highest winds ever recorded in Ireland, with gusts over 90 mph in Northern Ireland (CBS News).
When the grid is down for a week, your generator stops being a backup and becomes your only supply. That’s exactly when an unserviced machine is most likely to let you down.
Why generators fail in cold weather
Cold weather finds every weak point in a generator that’s been sitting idle since spring. The most common culprits are:
- Batteries. Flat or ageing starter batteries are the single most common reason a generator fails to start. Cold cuts battery capacity, and a tripped charger breaker can leave a battery quietly draining for months.
- Diesel fuel. Summer-grade diesel can wax and gel in low temperatures, blocking filters. Fuel left standing also collects condensation and contamination.
- Block heaters. Heaters work hardest in winter, which is when they fail most often — leading to low coolant temperature alarms or the engine failing to crank.
- Oil and coolant. Cold thickens oil and strains the engine on start-up, while weak antifreeze risks frost damage.
- Changeover and controls. A faulty automatic transfer switch (ATS) or controller means the set may never get the signal to start.
Your winter generator servicing checklist
A full winter service should cover each of these before the first named storm arrives:
- Test and load-check the battery — replace it if it's over three years old or struggling to hold charge, and confirm the charger is powered and working.
- Clean and tighten battery terminals to stop corrosion causing a weak crank.
- Check fuel quality and level — drain water from the tank, swap to winter-grade diesel or add an anti-gel additive, and keep the tank topped up.
- Replace fuel, oil and air filters so contaminated fuel can't starve the engine.
- Change the oil to a grade suited to low temperatures.
- Test coolant strength and top up antifreeze to the manufacturer's spec.
- Check block and battery heaters are working.
- Inspect belts, hoses and exhaust for cracks, leaks or blockages.
- Test the ATS and control panel, including remote start and alarms.
- Run a load bank testto prove the set can carry its full rated load, not just tick over.
- Weatherproof the enclosure— check seals, louvres and drainage so wind-driven rain and snow stay out.
Who needs a winter service most
Any generator benefits from a pre-winter check, but some users can’t afford a failed start:
Farms
Milking, ventilation and water pumps can't wait a week for the grid.
Care homes, surgeries and pharmacies
Heating, medical equipment and cold storage depend on continuous power.
Construction sites and events
Site welfare, lighting towers and security rely on portable sets running through dark, wet months.
Hire fleets
Every unit going out on winter hire should be serviced before it leaves the yard.
Rural homes and businesses
Overhead lines in exposed areas are often the last to be reconnected after a storm.
Frequently Asked Questions
September to November is ideal, before named storms usually arrive. That leaves time to source parts if anything needs replacing.
Most manufacturers recommend at least one full service a year, or by running hours for sets that work hard. Standby generators should also be exercised regularly between services.
Diesel doesn’t freeze solid, but it can wax and gel in low temperatures and block the fuel filter. Winter-grade diesel or an anti-gel additive prevents this.
The most likely cause is a weak or flat battery. Gelled fuel, a failed block heater or thick oil are the next things to check.
A load bank test runs the generator at its rated output using an artificial load. It proves the set can carry your site’s full demand, not just start and idle.
Book your winter generator service with MacGen
The next big storm won't give much notice, and engineers get booked up fast once the first warnings go out. Get your generator serviced now so it's ready to run for as long as you need it.
Contact the MacGen team today to book your winter generator service.