Lawn mower servicing is one of those jobs that's easy to put off. The mower starts, it cuts grass, so it must be fine — right? Usually, yes. Until the day it isn't, and you're stuck with a mower that won't start halfway through the season, or one that's cutting so badly your lawn looks worse after mowing.
The good news is that most mower servicing is straightforward DIY. You don't need a dealer for the vast majority of it, and the whole job takes less than an hour once a year.
Service your mower once a year — either at the end of the season before winter storage, or at the start of the season before first use. I prefer end of season because the mower goes into storage clean and prepped, and it's ready to go in spring without any faffing about.
If you mow heavily — large garden, twice a week, commercial use — service every 25–50 hours of use, or roughly every two to three months during the season.
Here's what a proper annual service covers, roughly in order:
Old oil contains metal particles, combustion acids, and moisture that corrode engine internals over time. Drain the old oil while the engine is slightly warm, then refill with fresh SAE 30 or 10W-30 (check your manual). Most walk-behind mowers take 400–600ml.
How often: Once per season minimum. Every 50 hours for heavy use.
Pull the spark plug and inspect it. A light tan or grey colour is healthy. Black, oily, or heavily crusted plugs should be replaced. Even if it looks okay, a new plug every season is cheap insurance — they cost £3–5 and take two minutes to fit.
How often: Inspect annually. Replace annually or every 100 hours.
A clogged air filter restricts airflow to the engine, causing poor performance, hard starting, and increased fuel consumption. Paper filters should be replaced. Foam filters should be washed in soapy water, dried, and lightly oiled.
How often: Clean every 25 hours. Replace paper filters annually.
A dull blade is the number one cause of a poor-quality cut. Sharpen the blade at least once per season — more often if you mow frequently. Replace it if there are deep nicks, bends, or cracks.
How often: Sharpen every 20–25 hours of mowing. Replace as needed.
Scrape all caked grass from the underside of the deck. Built-up grass reduces cutting efficiency, restricts airflow (which affects collection and mulching), and holds moisture that causes rust.
How often: Ideally after every few mows. Thoroughly at annual service.
Check the fuel line for cracks, the fuel filter for blockages, and drain old fuel if the mower has been sitting unused. With E10 petrol now standard in the UK, fuel degrades faster — don't use petrol that's been in a jerry can for more than 30 days.
How often: Check annually. Replace fuel lines every 2–3 years.
If your mower is self-propelled, check the drive belt for wear and the drive cable for correct tension. A slipping drive belt is a common issue that's cheap to fix but annoying if it goes mid-mow.
How often: Check annually. Replace belts every 2–3 seasons or when slipping.
Lubricate wheel bearings and height adjustment levers. Check for play in the wheels — worn bearings cause an uneven cut. A squirt of light machine oil on each axle takes seconds.
How often: Lubricate annually.
Cordless mowers are simpler — no engine, no oil, no spark plug, no fuel system. Your annual checklist is shorter:
Almost everything on the annual checklist is DIY-friendly. Here's where to draw the line:
| Job | DIY? | Notes |
|---|---|---|
| Oil change | Yes | Easiest job on the list |
| Spark plug | Yes | Just need a plug spanner |
| Air filter | Yes | No tools needed |
| Blade sharpening | Yes | File + vice is all you need |
| Deck cleaning | Yes | Scraper + elbow grease |
| Drive belt replacement | Maybe | Varies by model — some are fiddly |
| Carburettor cleaning | Maybe | Easy on simple carbs, tricky on others |
| Engine rebuild / valve adjustment | No | Dealer or small engine mechanic |
| Electrical fault diagnosis | No | Safety risk — use a professional |
If you'd rather have someone else do it, expect to pay:
Whether that's worth it depends on your comfort level. Personally, I do my own servicing — the parts cost about £10–15 per year and the whole thing takes under an hour. But if you've got a ride-on or a premium mower under warranty, a dealer service gives you peace of mind and a paper trail.
Between annual services, there are a few things worth keeping an eye on:
| Task | Frequency |
|---|---|
| Deck scrape | Every 2–3 mows (every time if wet) |
| Blade sharpen | Every 20–25 hours / 4–6 mows |
| Oil level check | Every 5 mows |
| Full annual service | Once per year (end of season ideal) |
| Blade replacement | Every 1–2 seasons |
| Drive belt check | Annually |
Keeping on top of mower maintenance isn't glamorous, but it's the difference between a mower that lasts three years and one that lasts ten. Most of it takes minutes, costs almost nothing, and you'll notice the difference in cut quality straight away.
