Lawn Mower Won't Start: Causes & Fixes

Faulty Spark Plug

There is fuel in the tank but your lawn mower still won't work? A dirty or corroded spark plug may be the culprit. Spark plugs do not last indefinitely, so remove the spark plug and inspect it carefully.

If you are unsure where the spark plug is located, consult the owner's manual for your mower. It will tell you where to find it, how to remove it, and how to clean it. In many cases, wiping the spark plug with a cloth is sufficient. Make sure there is no rust or dirt on the contacts in particular, as these need to be clean to allow the spark to jump.

If the mower still won't start, replace the spark plug with a new one. Make sure you purchase a spark plug that is compatible with your specific mower model.

Your Lawn Mower Has Been in Storage for a Long Time

Lawn mowers are often left unused over the winter months, which frequently causes starting problems come spring. After a prolonged period of storage, oil can settle and build up in the internal pipework. Pipes that are not properly lubricated often cause starting difficulties. We have compiled tips on how to winterise your lawn mower separately.

Ideally, the problem will resolve itself after several attempts to start the engine. Your owner's manual may also describe steps to remedy the issue.

Dirty Air Filter

Every lawn mower needs a clean air supply to start, and this is the job of the air filter. It prevents dust and dirt from entering the carburettor. The air filter cannot do its job properly if it becomes clogged with dirt — in which case the engine will cut out and the mower won't start.

A dirty air filter is perfectly normal. Over time, dust, oil, and debris will accumulate. It is therefore good practice to clean the filter regularly.

To remove the air filter correctly, refer to your owner's manual. If it is a paper filter, tap it gently to dislodge debris or clean it with compressed air. Foam filters can be washed with washing-up liquid and warm water. For a dual filter, it is advisable to replace the paper section when it becomes dirty. As a general rule, the mower should be cleaned regularly to prevent breakdowns.

After cleaning, allow the air filter to dry thoroughly before reassembling and refitting it.

Blocked Blades

You pull the starter cord and nothing happens. A likely cause is stones or twigs jamming the blade. This is often noticeable because the cord requires more effort than usual to pull. Now take a look underneath the mower — but first disconnect the spark plug lead or the mains cable. For a petrol-powered mower, make sure the fuel cap is closed. Remove any grass clippings, stones, and other debris blocking the blade. Ideally, wear gloves to protect yourself from the blade edges.

Replacing the blade is not a complicated job. We have outlined how to do this in our guide "How to Sharpen Lawn Mower Blades". It is also important to ensure you fit the correct blade for your mower. A blade that is not compatible can cause damage to the machine.

Clogged Fuel Filter

The fuel filter's job is to trap impurities in the fuel so they do not restrict the flow of petrol to the carburettor. This means that a dirty fuel filter will result in too little — or no — petrol reaching the carburettor, preventing the mower from starting.

To fix this, close the fuel tap and open the filter. Clean the filter element with compressed air or replace it. Close the filter and reattach the fuel line.

Dirty Carburettor

The carburettor is where petrol and air are mixed to create a combustible mixture. If the carburettor is dirty, the needle that regulates the fuel supply will not function correctly. This results in a mixture that can no longer ignite. A faulty or missing air filter or fuel filter is often the underlying cause.

The solution is to clean the filters mentioned above. Then open the carburettor and clean it with a brush before reassembling it correctly.

Electric Lawn Mower – Mower Won't Start

Electric lawn mowers often present similar problems to petrol-powered models. Issues such as running out of petrol, spark plug faults, and problems with the throttle cable do not apply, of course. Problems with electric mowers are more commonly caused by wear and tear, blockages, or cable damage. The same applies to axles and wheel bearings.

As diagnosing faults on an electric mower requires specialist knowledge and skill, repairs are best left to a qualified professional. Blockages and dirt can usually be cleared fairly easily.

If the mower won't start, it is often simply a case of the plug not being properly inserted into the socket, or a fault with the power cable. You should also check that the fuse has not blown.

For the sake of your own safety, do not attempt to repair damaged power cables yourself. Always contact a qualified electrician or specialist for this type of problem.

An important safety point with this type of mower: always disconnect it from the mains before carrying out any checks or cleaning. Failing to do so puts you at serious risk of injury.

Common causes of cable damage on electric lawn mowers include:

• Damage caused by the cutting blade,
• Damage caused by animals,
• Cable breakage due to incorrect winding,
• Damage caused by adverse mechanical force.