Ryobi 18v String Trimmer Troubleshooting – Fix 8 Common Problems

Ryobi is one of our favorite brands for yard tools. Their products are less expensive than many out there and often function as well as the professional brands for light to medium-duty jobs.

Of course, there is a downside to choosing these less expensive options. And that is that they often run into little glitches and problems. This is especially true, we’ve noticed, with the Ryobi 18v string trimmer.

Luckily, many of the common issues seen with this tool can be easily fixed with a few simple steps.

In our Ryobi 18v string trimmer troubleshooting guide, we’ll look at the most common problems with this tool and walk you through how to fix them.

1. Ryobi 18V Trimmer Won’t Start

If your Ryobi 18v weed wacker won’t start when you depress the switch trigger, the problem is most likely due to the batteries, a connection issue, or a mechanical problem. Luckily, most of these are easy to fix with a few short steps.

The shaft isn’t connected completely

If the shaft is not securely connected at all points, the power from the battery can’t reach the motor to turn it over.

  1. Uncouple the shaft connection.
  2. Clear away any debris.
  3. Recouple and twist into place until you hear the click.

The battery pack isn’t secured

If the battery pack isn’t connected completely, it won’t make good enough contact with the terminals to start the motor.

  1. Remove the battery.
  2. Clear away any debris on the battery and head terminals.
  3. Resecure the battery, pressing until you hear the click.

The battery isn’t charged

If the above solutions don’t work, your trimmer most likely won’t start because the battery does not have enough juice to turn over the motor.

  1. Remove the battery and place it on the charger.
  2. The charging indicator light should start blinking. If you get an error or the light does not come on, see #6 below.
  3. Wait until the battery is completely charged before trying again.

Broken connection

Multiple wires connect the battery terminal and switches in the handle to the motor in the head of the trimmer. If any of these connections break, the motor won’t engage.

The most likely wire to become disconnected is the white wire that connects the motor to the shaft. Luckily, this is an easy problem to check and fix.

  1. Remove the screws in the trimmer head to open it up.
  2. Carefully lift off one side and examine the wiring inside. The two black wires should be securely connected, as should the white wire from the shaft and the red wire from the motor, as shown in the diagram below.
  3. Ensure all connections are secure, then close the housing and test. 
  4. If this doesn’t work, there may be a loose connection in the handle. Remove the screws in the handle to open it up. 
  5. Assure all connection points (see picture below) and securely connected.

Note: If none of these solutions work, then it’s likely one of your components has burnt out or malfunctioned. Contact the manufacturer for a replacement if the unit is still under warranty.

2. Ryobi Cordless String Trimmer Stalls

Electric trimmers like this one stall for one reason: something is overheating, causing one of the temperature sensors to switch the unit off to avoid damage. Overheating is typically caused by vent blockage around the battery contact plate, around the motor, or a problem with the motor itself.

Dirty air vents

The 18v electric trimmer doesn’t have an air filter like the gas version. But it does have air vents around the motor and battery contact plate (on some models) that can become blocked with debris.

  1. Visually check for debris stuck in the vent holes around the contact plate (located just below where the battery attaches) and around the motor (above the spool housing, in most models). Manually remove what you can.
  2. Use a shop vacuum with a brush attachment to clear away fine debris from both vents.

Malfunctioning motor or contact plate

If cleaning the vents does not help, then there is likely a problem with the motor or contact plate. Your best bet here is to call the company, especially if the unit is still under warranty.

If it’s not under warranty, try these steps:

  1. Identify which end the problem is occurring in by feeling for obvious heat buildup after the unit stalls out. If the handle is hot, your problem is the battery contact or associated switch. If the head is hot, the motor is likely the issue.
  2. Open the handle or motor head (whichever is overheating) by removing the necessary screws.
  3. Examine the part for obvious damage or dysfunction. If everything looks normal, use a can of air to remove any debris that’s built up.
  4. Resecure the housing and test.

If this doesn’t work and the motor and battery contact appears to be in good working order, you may be able to create a workaround by installing an external fan to help keep the problem area cool. There are many DIY options for this described on the web, including this simple hack that uses two 24-volt fans.

3. Runs Rough

A rough-running gas trimmer can be caused by a plethora of issues. Luckily, with an electric unit, the causes are far fewer. In fact, a rough-running Ryobi 18v trimmer that chugs, slows, and speeds up without input, is likely suffering the same issues as one that stalls completely.

If your trimmer is experiencing this problem, it’s important to act fast before the issue becomes worse and causes the tool to stall.

Start by cleaning the vents as described above. If that doesn’t work, open the motor compartment and handle and clean and inspect the motor and battery contact.

4. Ryobi Line Trimmer Head Won’t Spin

man opening the head of a Ryobi 18v string trimmer

If the head of your trimmer suddenly stops spinning mid-use or doesn’t start spinning when the unit is turned on, you likely have one of two problems. Either the string is bound up in the spool and physically preventing the head from spinning, or the motor is not engaging with the trimmer head.

Bound-up spool

A bound-up spool can quickly overtax your trimmer and cause damage to the motor, so it’s important to turn the trimmer off immediately if the head stops spinning. From there, you can easily identify and solve the issue.

  1. With the trimmer powered off, remove the string head.
  2. Open the spool as you would to install a new string (see video below).
  3. The tangled string will be obvious. Unwind it manually and rewind the string cleanly, then reinstall the spool and try again.

If you don’t see any obvious tangles in the line, then the issue is likely a problem with the motor. You can buy a replacement motor online through various retailers using your tool’s model number.

Note: If you don’t see any obvious tangles in the line, then the issue is likely a problem with the motor. You can buy a replacement motor online through various retailers using your tool’s model number.

5. Ryobi 18V Trimmer String Line Won’t Feed

close-up of an electric trimmer’s string line

There are a number of reasons that your auto feed spool can fail or that you cannot advance the line manually. Luckily, the fix for each issue is generally pretty straightforward.

Note: Make sure the trimmer is powered off before attempting these fixes.

  • The line is too short. If the string has been sheared off too short to engage the auto feed, use needle nose pliers to manually pull on the string while depressing the feed button.
  • The line is tangled. If the line cannot be advanced manually, a tangle is likely. Remove the string housing and rewind the string cleanly.
  • The string has welded to itself. If you cannot easily unwind the string to rewind it (and it is not obviously tangled), try lubricating it with some silicone spray, replacing the spool, and then advancing it manually.
  • The string has run low. If there isn’t enough string left on the spool to advance, replace it with a fresh spool.

If troubleshooting issues with the string does not solve the problem, there may be something wrong with the string housing itself. You can contact customer service for a replacement part or order an aftermarket replacement yourself.

6. Ryobi Cordless Weed Wacker Battery Won’t Charge

photo showing how to connect a Ryobi battery

By far, one of the most common problems with Ryobi products is with the batteries not charging. If you get the blinking lights of death when you place your batteries on the charger, one of four common issues is likely to be the problem.

Batteries are too hot or cold

If you’ve just pulled your batteries off the trimmer after a long job, it’s possible they won’t charge because they’re too hot. Try placing them in the fridge for about ten minutes and then trying them on the charger again.

If the batteries have been in storage in the garage or shed, then it’s possible they’ve gotten too cold to charge. Bring them inside and let them warm up to normal room temperature before trying to charge them again.

Corroded or dirty terminals

If the terminals on your battery or charging dock are dirty, the battery won’t charge. This type of charging failure usually does not elicit the blinking lights of death because the charger won’t register that the battery has been loaded.

For corroded terminals, use a piece of fine sandpaper to remove the corrosion.

If dirt or debris is the problem, use a wire brush and alcohol wipes to get them clean. Then try loading the battery again.

Faulty charger

It’s possible the problem is not your battery but the charger.

To test this theory, bring one of your batteries to the closest home improvement store and test it on one of their battery chargers. If it works, you might as well buy a new charger while you’re there because yours has likely failed.

The battery is in sleep mode

This is by far the most common cause of battery failure in Ryobi batteries (but also the most time-consuming to troubleshoot, which is why we saved it for last).

When batteries are stored dead, it’s possible for the power to drop so low that the charger can’t detect whether the battery is healthy or not. To avoid damage, the charger won’t connect to these batteries to charge them. Most chargers have a boost feature that overcomes this, but not Ryobi chargers.

If your battery has entered sleep mode, you’ll need to get it back to the minimum power level before you can charge it regularly. The easiest way to do this is with micro charges.

  1. Place the battery on the charger, then count how long it takes for the lights to start flashing.
  2. Remove the battery.
  3. Place the battery back on the charger and start counting, removing it one second before the lights would have started flashing.
  4. Repeat this step multiple times until the charger flashes green and begins charging the battery normally.

If this doesn’t work to wake your battery up, there are other options for boosting a sleeping battery. You can check our guide on how to fix common Ryobi 40v battery problems.

7. Engine Emits Smoke

There are many stories of Ryobi trimmers smoking, both from the motor and the handle. When this happens to an older model, it is typically a sign of wear and subsequent motor failure. In newer units, it is likely a matter of a manufacturer defect.

Since a smoking trimmer has the potential to catch fire, you should immediately turn the trimmer off and remove the battery if you see or smell smoke. Leave the trimmer to cool on the sidewalk or driveway, away from flammable debris.

For new trimmers, contact the store you purchased it from or the manufacturer right away. It should be covered under the manufacturer’s warranty, and they will replace it. For older models, you can try replacing the motor but proceed with caution.

8. Grass Wraps Around String Head

Tall grass can easily become wrapped around the boom housing and string head, causing it to stall. This is especially likely to happen when you’re trimming long, wet grass. Luckily, there are a few tips you can follow to reduce how often this happens:

  • Always trim tall grass from the top down. Move the trimmer back and forth over the grass, taking a few inches off with each pass until you get to the ground rather than starting at ground level.
  • Use higher speeds when trimming tall grass. This will help assure the grass blades are cut and thrown away instead and being bent and pulled into the housing.
  • Wait until the grass dries. Dry grass is much less likely to bend and get sucked into string housing than wet grass.

If you’re still struggling to get your Ryobi 18v string trimmer to run well after completing this troubleshooting guide, then it may be time to purchase a new trimmer. Our battery powered string trimmer reviews can help!

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Aaron Green
Aaron is the founder of and Essential Home and Garden. He likes to spend his spare time with his family, and doing DIY projects in the home and garden.

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