By the UK Generator Guide — Home Petrol Generator Reviews & Advice Team · Updated May 2026 · Independent, reader-supported

Petrol Generator for a Power Cut UK: What You Need & How to Prepare

Power cuts in the UK are becoming more frequent, whether from severe weather, infrastructure issues, or maintenance work. A petrol generator can provide essential backup power, but buying one without proper planning often leads to disappointment—either it's too small to be useful, or too large and expensive to justify. Here's what you actually need to know.

Which Appliances Really Need Power?

Before you buy, identify what matters most to your household. You won't run everything, so be realistic.

Essential to consider:

• Boiler (most UK homes need this for heating and hot water)
• Fridge and freezer (food safety is critical)
• Central heating system or electric heater
• Lights and charging points
• WiFi router (for information and emergency services contact)

Nice to have but power-hungry:

• Cooker or oven
• Dishwasher
• Washing machine
• Tumble dryer
• Multiple heaters running simultaneously

The boiler is often the biggest challenge. Most modern condensing boilers draw 300-500W to run, plus a brief power surge on startup. Your generator must handle that initial surge—typically 2-3 times the running wattage.

How Much Power Do You Actually Need?

Wattage adds up quickly. A typical kettle uses 3kW; a toaster 2-3kW. You can't run both simultaneously. A 3kW generator will handle your boiler, fridge, and lights with careful management. A 5kW generator gives you genuine flexibility—you could theoretically run the boiler plus a heater, or boiler plus some kitchen appliances.

Work out your own scenario. Check appliance wattages (usually on a label or in the manual). Add up what you'd realistically need running at the same time during a genuine power cut—probably boiler plus essential lighting and the fridge. That's your minimum.

Most homeowners find 3kW sufficient for essentials and 5kW genuinely comfortable for short-term outages. Larger generators (7kW+) become expensive, heavy, and overkill for occasional UK power cuts lasting hours, not days.

Runtime: The Real Problem

A 3kW petrol generator typically burns 1-1.5 litres of fuel per hour at reasonable load. A 5kW burns 2-3 litres per hour. That means a 15-litre fuel tank—standard for most home generators—gives you roughly 10 hours at 3kW or 5-7 hours at 5kW. Running at quarter-load (just boiler and fridge) nearly doubles runtime.

Most UK power cuts resolve within 4-6 hours. Longer outages are rare unless there's been genuinely severe weather. Plan for 8-10 hours of fuel as a comfortable buffer, which is realistic for decent-sized generators.

Safe Storage Matters

Petrol degrades. Fuel left in a generator's tank for months turns to varnish, clogs the carburettor, and prevents it starting. This is the number one reason home generators disappoint when actually needed.

Proper storage approach:

• Run the generator under load for 10-15 minutes monthly
• Use fuel stabiliser (such as Sta-Bil) if storing longer than two weeks
• Store fuel in approved jerry cans in a well-ventilated shed or garage, never indoors
• Keep fuel separate from the generator itself
• Date your fuel containers

If you won't commit to monthly running, drain the tank completely and run the engine until it stops, then restart occasionally without fuel to keep the carburettor clear.

Testing Before You Need It

Never assume your generator will start during an actual power cut. Doing so is asking for trouble.

Monthly routine:

• Check oil level (most generators won't start if oil's low)
• Start under no load, let it run 5 minutes
• Connect a small load (a lamp or kettle) for 10-15 minutes
• Check for leaks, unusual sounds, or vibration

Annually:

• Replace spark plugs
• Check the air filter (dirty filters cause starting problems)
• Run a full test under a realistic load (boiler, fridge, lights) for 30 minutes

A generator that hasn't run in months won't start when you're sitting without heat, light, or hot water. Monthly testing takes 20 minutes and prevents that scenario.

Practical Points Worth Knowing

Petrol generators are noisy—typically 80-90 decibels. They're fine in your garden during a daytime test, but running one for hours in winter is unpleasant. Place it outside if possible, with fuel and power cables run indoors through a door or window.

Petrol generators can't safely run indoors or in garages, even with the door open. They produce carbon monoxide, which kills silently. Always operate outside.

Startup isn't instant. In cold weather, a petrol generator may take several pull-cord attempts to start. Dual-fuel models (petrol or LPG) start more reliably in cold conditions, though they're pricier.

Choosing Your Size

A 3kW generator is genuinely portable—around 40kg, fits in a car boot—and handles boiler plus essentials reliably. Good for renters or those with limited storage.

A 5kW generator is semi-portable (60-70kg) and genuinely functional for short outages. You can run the boiler plus heating or multiple kitchen circuits. Costs more upfront but gives real peace of mind.

Anything larger becomes a fixed installation, heavy, and overkill for the typical UK power cut lasting a few hours.

The Bottom Line

A petrol generator is genuinely useful backup during UK power cuts, but only if properly sized, maintained, and actually tested. Plan for what you'd realistically need (usually boiler plus essentials), invest in a 3kW or 5kW model from a respected manufacturer, commit to monthly testing and fuel management, and you'll have working backup power when the grid fails.

Neglect the maintenance, let fuel degrade, or skip testing, and you'll discover—at worst possible moment—that your generator won't start.