| Petrol mower will not start | - Stale fuel or blocked carburettor
- Fouled spark plug
- Blocked air filter
- Sheared flywheel key
- Low compression
| - Fresh fuel? Old petrol is a frequent suspect after winter, but only one of several.
- Pull the plug: wet, sooty or clean; check there is a spark only outdoors and away from fuel.
- Air filter: clogged with dust or soaked with oil after being tipped the wrong way.
- Does the engine turn with even resistance?
| - When it last ran.
- How it was stored and with which fuel.
- Whether it hit something before it stopped.
| Basic to Advanced, depending on the cause Diagnosis time: 1–3 hours Safety-relevant | Plug, filter, fuel and a carburettor clean are cheap in parts and cost time. A sheared flywheel key needs a puller and the right torque. Low compression means internal wear — not economic on most used mowers. | - Little or no compression.
- Oil full of petrol, or milky.
- Stopped dead after hitting something.
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| Starter cord broken, stuck or will not retract | - Broken starter rope
- Broken or unhooked recoil spring
- Seized engine
- Bent crankshaft
| - Plug lead off. Turn the blade carefully by hand with a glove: the engine must turn freely.
- Look at the rope: frayed, snapped, or intact but not retracting.
- Check whether the starter housing comes off with a few screws on this engine.
| - Engine model and type numbers.
- What happened when the cord failed.
| Intermediate to Professional, depending on the cause Diagnosis time: Under an hour Safety-relevant | Rope is cheap and, on many engines, replacing it is a described owner job. The recoil spring stores energy and can fly out when the pulley is lifted — wear eye protection and follow the engine maker’s procedure. A broken spring or pawls usually mean a complete starter assembly. | - Engine will not turn by hand.
- Cord fault combined with heavy vibration history.
- No manual or parts for that engine.
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| Heavy vibration | - Bent blade
- Bent crankshaft
| - Plug lead off. Look at the blade tips: is one higher than the other relative to the deck?
- Look for a bent or chipped blade and fresh impact marks under the deck.
- Watch the blade bolt or crank end as someone turns the engine slowly by hand: any wobble is the crankshaft.
| - Whether it hit a stone, stump or kerb.
| Intermediate to Professional, depending on the cause Diagnosis time: Under an hour Safety-critical | A blade is a routine part, fitted to the correct torque. A bent crankshaft is not economic to repair and is dangerous to run. | - Any crank wobble.
- Cracked deck around the engine mounts.
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| Handle, knob, spool or guard missing | - Wear part missing
- Guard missing
- Drive or gearbox fault
| - List what is missing against the manual’s parts diagram.
- Check every guard and safety switch is fitted and works.
- Run the machine: does the drive actually turn the head, chain or blades?
| - Make and model.
- Why the part is missing.
| Basic to Advanced, depending on the cause Diagnosis time: Minutes Safety-critical | Spools, line heads, handles and knobs are wear parts on many machines, but fit is machine-specific. A missing guard must be replaced with the correct part before any sale. | - Guard unavailable for that model.
- Drive or gearbox fault.
- Chainsaws with chain-brake or chain-catcher problems.
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| Pressure washer leaks at hose, gun or connector | - Worn O-ring or connector
- Damaged high-pressure hose
- Damaged pump
| - Run it with water connected and find the exact leak point.
- Check O-rings at the hose, gun and lance connections for cuts and flattening.
- Bend the high-pressure hose along its length looking for bulges and cuts.
| - Model and rated pressure.
- Whether it was stored frost-free and drained.
| Basic to Professional, depending on the cause Diagnosis time: Under an hour Safety-relevant | O-rings and connectors cost very little. A hose costs more and must be rated for the machine’s pressure with the correct fittings. Water from under the body means pump seals or a cracked pump. | - Water coming from inside the body.
- Hose or gun of unknown rating fitted.
- Stored outdoors through frost.
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| No pressure, pulsing, or motor only hums | - Blocked nozzle or inlet filter
- Damaged pump
- Mains, switch or capacitor fault
| - Inlet filter clean? Nozzle clear? Tap fully open and hose not kinked?
- Let water run through with the motor off to bleed air, then try again.
- Listen: a motor that only hums is not a nozzle problem.
| - What it did when it last worked.
- Storage over winter.
| Basic to Professional, depending on the cause Diagnosis time: Under an hour Safety-critical | Filters and nozzles are trivial. Pump seals, valves and unloaders are dismantling jobs with model-specific kits. Motor, capacitor and switch faults are mains electrical work. | - Motor hums or trips the supply.
- Pressure still absent with clean filter, clear nozzle and air bled.
- Cracked pump housing.
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