Insect Killers & Repellents: Common Problems & How to Fix Them
Published 2026-08-01 · Updated 2026-08-01
The Nest & Yard editorial team
Written and reviewed by our UK-based team of home improvement and gardening writers, who research specs, pricing and customer reviews before every recommendation. Reviewed and updated on 2026-08-01.
Our pick: the Virbac Indorex Defence Flea Spray for the Home | Kills Fleas | 500ml Can | Kills Cat & Dog Adult Fleas and Dust Mites in the Home on Contact, up to 12 Months Protection — the best Insect Killers & Repellents we tested, from £13.99.
Persistent insects can quickly turn a comfortable home into a frustrating battleground, and many insect killers and repellents require careful use to deliver their intended results. If you’re experiencing issues with products like flea sprays, fly killers or mosquito repellent plugs – perhaps noticing inconsistent coverage or a lack of effectiveness – it's important to systematically check the basics before contacting customer support. This guide focuses on straightforward diagnostic steps for common problems encountered when using insect control solutions, covering things such as correct placement, battery life, and ensuring appropriate settings are applied, all relevant whether you’re using a single can or multiple refills.
See the full range in Insect Killers & Repellents.

#1 Pick
Virbac Indorex Defence Flea Spray for the Home | Kills Fleas | 500ml Can | Kills Cat & Dog Adult Fleas and Dust Mites in the Home on Contact, up to 12 Months Protection- Aerosol Spray
£13.99
Pros
- UK No.1 household flea spray, award-winning with pet owners
- Kills fleas and dust mites on contact with up to 12 months protection
- Treats a full 3-4 bedroom house from one 500ml can
Cons
- Room needs airing out for a while after spraying

#2 Pick
Raid Rapid Action Fly & Wasp Killer, Fly Killer Spray for Indoor Use, 300ml- Aerosol Spray
£3.99
Pros
- Rapid knockdown of flies and wasps on contact
- Compact 300ml can fits in a kitchen cupboard
- Widely available, well-known trusted brand
Cons
- Strong odour immediately after spraying

#3 Pick
Raid Rapid Action Fly & Wasp Killer, Fly Killer Spray For Indoor Use, Pack of 6 (6 x 300ml)- Aerosol Spray
£16.84
Pros
- Bulk pack of 6 cans works out cheaper per can
- Rapid knockdown of flies and wasps on contact
- Well-known trusted brand
Cons
- Bulkier to store than a single can
#4 Pick
Jungle Formula Indoor Mosquito Killer Plug-in Refill, Up to 45 Nights- Plug-In Mains Powered
£6.99
Pros
- Well-known pharmacy brand widely stocked across the UK
- Refill lasts up to 45 nights of use
- Vapour formula kills mosquitoes and biting insects indoors
Cons
- Requires a compatible Jungle Formula plug-in base unit
FAQ
My electric insect killer isn't turning on at all. What could be the issue?+
Firstly, check the power outlet to ensure it’s functioning correctly by plugging in another device. Then, verify that the unit is switched fully ‘on’ and that the cable is securely connected to both the device and the mains socket – a loose connection can prevent operation. If these checks are successful, consult the manufacturer's instructions or contact their support team as there might be an internal power supply problem.
The insect repellent isn’t spraying effectively; it’s just producing a weak stream.+
Inspect the nozzle for any blockages – debris, dust, or dried residue can restrict spray flow. Clean the nozzle thoroughly with warm water and ensure it's functioning correctly before attempting to use the device again. If cleaning doesn't resolve the issue, check the fluid reservoir level is sufficient.
My ultrasonic insect repellent is making a strange buzzing noise.+
Ultrasonic devices can sometimes produce unusual noises due to vibration; ensure the unit isn’t placed directly on a hard surface which could amplify the sound. Try moving it to a different location, away from reflective surfaces, and check that there aren't any loose parts rattling within the device casing – if noise persists, discontinue use and refer to the manufacturer’s guide.
The battery on my portable insect repellent isn't charging.+
Confirm that the charger is correctly plugged into both the device and a functioning mains outlet. Ensure the charging cable itself isn’t damaged or frayed; a faulty cable can prevent proper charging, and also check the charging indicator light to see if it illuminates when connected.
I've noticed liquid leaking from my electric mosquito zapper. What should I do?+
Immediately disconnect the device from the power source to avoid potential electrical hazards. Carefully examine the reservoir for any cracks or damage that may be causing the leak and discontinue use if leakage is significant, referring to the manufacturer’s instructions.
My insect repellent isn't spraying at all after cleaning it.+
Ensure the spray nozzle is completely dry before attempting to operate the device. Sometimes, even trace amounts of water can interfere with the propellant’s ability to generate a spray; allow sufficient time for thorough drying.
The remote control on my insect killing device isn’t working. +
Check that the batteries in the remote are fresh and correctly installed – weak batteries often cause unresponsive controls. Also, examine the infrared receiver on the device itself to ensure it's clean and unobstructed, as dirt or debris can interfere with the signal.
My ultrasonic insect repellent seems less effective than when I first bought it.+
Ultrasonic devices can lose effectiveness over time due to changes in ambient noise levels. Try relocating the device to a different room or area, away from other electronic equipment which might interfere with its operation. Clean the device’s exterior regularly to remove dust and debris.
I’ve tried cleaning my insect repellent but it still smells weak.+
Ensure you are using the correct amount of refill fluid as per the manufacturer’s instructions – insufficient fluid will naturally reduce spray strength. Check that the fluid is fresh and hasn't degraded; older fluids lose their potency over time.
My insect killer isn’t switching off automatically after use.+
Verify that the safety timer function is correctly set and hasn't been accidentally disabled. If the device has a manual ‘off’ switch, ensure it's fully engaged; some models have multiple power-saving modes which might require careful configuration.
In depth
The insect killer or repellent unit won’t turn on/start
There are several reasons why an electric insect killer or repellent might fail to switch on initially. The first thing to check is the power source – it’s surprisingly common for this to be overlooked. Begin by ensuring the device is fully charged if it's a battery-operated model, or that it's correctly plugged into a functioning mains outlet. Test the outlet with another appliance you know works, such as a lamp, to confirm the socket itself isn't providing power. Inspect the lead for any visible damage – cuts, fraying or bends can disrupt the electrical connection and prevent operation. A damaged plug could also be the culprit; ensure it’s firmly inserted into the wall outlet. If using an AC adapter, check that it is securely connected to both the device and the mains socket. Sometimes, the internal switch mechanism can become temporarily stuck, particularly if the unit has been stored in a damp environment. Gently pressing the power button for a few seconds might dislodge any debris or reset the internal circuitry. Finally, confirm the unit isn’t switched off via an on/off toggle switch; many models have this feature. If you've conducted these basic checks and the device remains unresponsive, it is vital to cease operation immediately. Electrical malfunctions can be dangerous, and continuing to attempt activation could pose a risk of electric shock or damage to the equipment. Contact either the manufacturer’s customer support line or a qualified electrician for assistance; attempting any internal repairs yourself would be ill-advised.
The insect killer or repellent isn't performing as expected
If your insect killer or repellent is producing limited results, it's important to consider factors that could be affecting its effectiveness. Firstly, check the battery level if the device operates on batteries – a low charge will significantly reduce its operational range and potency. Replace with fully charged batteries of the correct type, ensuring you follow the manufacturer’s recommendations regarding polarity. If using a mains-powered unit, verify that it's positioned correctly to effectively target insects; many models have adjustable nozzles or spray patterns that need to be aligned properly for optimal coverage. Consider the environment – strong winds can disrupt the spray pattern and reduce its reach. Additionally, ensure there aren’t any obstructions blocking the device’s line of sight to potential insect targets. Cleaning the nozzle and spray head is also essential; accumulated residue can impede the flow of repellent or insecticide, diminishing its effectiveness. Regularly check the filter (if applicable) as a clogged filter will restrict airflow and reduce the unit's output. If you have recently refilled the repellent reservoir, ensure it’s correctly sealed to prevent leaks and maintain consistent spray delivery. Should these adjustments fail to improve performance, it suggests a deeper issue with the device itself, requiring professional diagnosis. Electrical components may be malfunctioning or the internal mechanism could be damaged – consulting an electrician is crucial before further investigation.
Unusual noises emanating from the device
Strange sounds coming from your insect repellent or killer can indicate several potential problems. A high-pitched whining noise often suggests a motor malfunction within the unit, which can be caused by worn bearings or electrical interference. A rattling sound might result from loose internal components vibrating against each other – this could be due to accumulated dust or debris inside the unit. If you hear a buzzing sound, it’s likely an issue with the power supply, possibly caused by voltage fluctuations or a faulty transformer. Clicking noises can often be attributed to problems with the spray mechanism, perhaps related to air pressure or a blocked nozzle. In all cases of unusual noise, immediately cease operation and disconnect the device from its power source. These sounds are indicators of potential mechanical or electrical faults which could become more serious if left unchecked. Attempting to troubleshoot further yourself carries a risk of injury or damage to the unit. Seek advice from the manufacturer’s technical support team or contact an experienced appliance repair technician for assessment and repairs – particularly if there is any hint of electrical issues.
Leakage from the device
Detecting a leak in your insect repellent or killer requires immediate attention, not only to prevent potential damage but also due to safety concerns associated with some repellents. First, check the reservoir where the repellent is stored; ensure it’s properly sealed and that there are no cracks or leaks around the cap. Examine the spray nozzle for any signs of leakage – a damaged nozzle can cause the product to escape during operation. If using a battery-operated model, inspect the battery compartment for swelling or leaking batteries, which could compromise the device's electrical safety. Carefully examine the entire unit’s exterior for cracks or damage that might be allowing repellent to seep out. Clean any spilled repellent immediately with appropriate cleaning products – follow the manufacturer’s instructions for disposal of used repellent. If the leak persists after these initial checks, it likely points to a more serious internal problem within the device's construction. Electrical components and seals could be damaged, presenting a potential hazard if the unit is exposed to moisture. Contact the manufacturer’s customer support team or a qualified appliance repair technician for evaluation – any attempt at self-repair would be highly inadvisable due to electrical risks.
The unit isn't charging (if applicable)
If your battery-operated insect repellent or killer isn’t charging, several factors may be involved. Begin by confirming that the charger is working correctly; test it with another compatible device to verify its functionality. Inspect the charging cable for any visible damage – cuts, fraying, or bends can disrupt the electrical connection and prevent charging. Ensure the charging contacts on both the unit and the charger are clean and free from debris; a buildup of dust or grime can interfere with the charging process. Try using a different power outlet to rule out issues with your existing socket. If the device has an indicator light, check if it’s illuminated while charging – this confirms whether the charger is receiving power. Some units have overcharge protection mechanisms which may temporarily halt charging when full; allow the unit to cool down and try again. In cases where charging consistently fails after these checks, it suggests a problem with either the battery itself or the internal charging circuitry within the device. Attempting to replace the battery yourself could void any warranty or lead to further damage – consult the manufacturer’s instructions for battery replacement guidelines or seek assistance from a qualified technician.
Cleaning difficulties and filter blockages
Maintaining regular cleaning of your insect repellent or killer is essential for optimal performance and longevity. The spray nozzle and surrounding areas can quickly become clogged with residue, reducing the effectiveness of the product dispersal. Use a damp cloth or cotton swab to gently clean the nozzle, ensuring you avoid applying excessive pressure that could damage it. Regularly inspect and clean the filter (if applicable), as a blocked filter will restrict airflow and diminish the unit's output. Remove the filter according to the manufacturer’s instructions and thoroughly wash it with warm water – avoid using harsh chemicals or abrasive cleaners. If cleaning proves difficult, consider using a small brush or pipe cleaner to dislodge any stubborn blockages. Ensure you allow the filter to dry completely before reinserting it into the unit. A build-up of debris can also affect the spray pattern and overall performance; regular cleaning helps maintain optimal operation.
Resetting the device
Many insect repellent or killer units incorporate a reset function, which can resolve minor operational issues. The method for resetting varies depending on the model, so consult the manufacturer’s instructions first. Typically, this involves pressing and holding a specific button for several seconds – often the power button – until the unit resets its internal memory. Some models may require disconnecting the device from its power source before initiating a reset. Following a reset, test the device to see if the issue has been resolved. If the problem persists after resetting, it suggests a more complex malfunction that requires professional attention.
Potential issues with settings and controls
The operation of your insect repellent or killer is governed by various settings and controls designed to optimise its performance and target effectiveness. Before contacting support, carefully review the device’s manual to ensure you're utilising the correct settings for your specific needs – particularly regarding spray pattern, intensity, and timer functions. Incorrect settings can lead to reduced efficacy or unintended consequences. Check that any adjustable nozzles are correctly positioned and aligned; even slight misalignments can affect the spray pattern. Ensure all controls are fully engaged and that there are no obstructions interfering with their operation. If you've recently adjusted the settings, try reverting them to the factory defaults to rule out user error as the cause of the problem.
Final checks and professional referral
After conducting these surface-level checks, if your insect repellent or killer remains malfunctioning, it’s crucial to recognise that further investigation requires specialist knowledge and equipment. Continuing to operate a faulty device poses potential risks – electrical shocks, chemical exposure, or damage to surrounding property. Cease operation immediately and disconnect the unit from its power source. Contact either the manufacturer's customer support line for technical assistance or consult with a qualified appliance repair technician – particularly if there are any signs of electrical faults or unusual behaviour. Do not attempt to open the device’s casing or work on internal components yourself, as this could void your warranty and create a safety hazard. Seeking professional help ensures that the problem is diagnosed correctly and repaired safely by someone experienced in handling these types of devices.