How to fix outdoor lighting faults: tripping, water and dead lights
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Mike's quick answer
Most outdoor lighting faults come down to water getting in, a sensor or timer set wrong, or a loose or corroded connection. Swap the bulb, clean the sensor and check the settings yourself. If the RCD trips more than once, there's water in the wiring, or you can smell burning, switch off and call an electrician.
Outdoor lights fail more often than indoor ones because they live in the rain, frost and sun, next to soil and spades. The faults are predictable, though. Nearly all of them come down to three things: water getting in, a sensor or timer that’s set wrong or failing, or a loose or corroded connection.
The symptom and the timing usually point to which. A light that trips the electrics after rain has water in it somewhere. A light that’s on all day is almost always the sensor, not the wiring. Some of this you can sort out yourself; some of it you shouldn’t touch. Both are covered below.
Quick fault finder
| Likely cause | Start with | |
|---|---|---|
| Nothing works | Tripped breaker or RCD, switch, timer, bulb | Consumer unit, switch and timer, then a bulb you know works |
| RCD trips after rain | Water in a fitting, junction box or damaged cable | Reset once only, then check the lowest fittings |
| RCD trips instantly on reset | Serious insulation fault | Leave it off and call an electrician |
| One light dead, rest fine | Bulb, driver or that fitting's connection | New bulb first, then the fitting |
| On all day | Dusk setting, dirty photocell, override mode | Clean the sensor, reset the settings |
| Comes on by itself | Sensor seeing branches, cars, pets or a flue | Lower sensitivity, re-aim the sensor |
| Flickers, or glows when off | Loose connection, failing driver, incompatible control | Good-brand LED bulb, then check the control |
| Water inside | Failed seal or cable entry, wrong IP rating | Switch off; usually replace the fitting |
What you can safely check yourself
Before you look at any fitting, switch the circuit off at the consumer unit, not just at the wall switch. Many PIR and dusk-to-dawn lights have a permanent live feed, so the terminals can be live even when the light is off. If the light is on a fused spur, switch that off and take the fuse out too. For plug-in garden lighting, unplug the transformer.
With the power off, these are reasonable homeowner jobs:
- Swap the bulb for one you know works.
- Clean the PIR lens and photocell with a soft damp cloth.
- Reset timers, sensor settings and smart schedules.
- Look for cracks, water, rust and loose cable glands, and tighten a loose gland or cover screw.
- On a 12 V system, check the plug-in transformer, its timer and the connectors along the run.
Stop there if you’d need to open a junction box, disconnect fixed wiring or dig up a cable, unless you’re competent to isolate and test it. And stop immediately if the RCD won’t stay on, there’s water in the wiring, or you see scorching or smell burning.
The RCD keeps tripping
A tripping RCD isn’t the fault; it’s the RCD doing its job. It watches for electricity leaking to earth and cuts the power within a fraction of a second, fast enough to greatly reduce the risk of a fatal shock. Outdoors, that leak is usually water bridging a connection inside a fitting or junction box, or a damaged cable.
Reset it once. If it trips again straight away, leave it off. Resetting a circuit with water in it again and again makes the damage worse, and Electrical Safety First is clear that an RCD that keeps tripping means a fault that needs investigating.
You can narrow it down without opening anything. Unplug anything in the outdoor sockets, including garden lighting transformers. If one RCD covers several circuits, switch off all the breakers it protects, reset the RCD, then switch the breakers back on one at a time; the one that trips it is the circuit with the fault.
If it only trips after rain, start with the lowest and most exposed points, with the power off: ground lights, spike lights, bollards, and any junction box near soil level. A fitting with water sitting in it is your answer. If nothing obvious turns up, an electrician will run an insulation resistance test, which finds leaks you can’t see, including damaged buried cable.
Water inside the light
A light mist on the inside of the glass that clears once the light has been on for a while is condensation. It happens as fittings warm up and cool down, and on its own it isn’t a fault. Droplets that stay, water pooling in the base, tide marks or rust are water getting in, and that’s not normal.
The usual ways in are a fitting with too low an IP rating for where it is, a perished or badly seated gasket, a cable gland that isn’t tight or doesn’t suit the cable, water running down the cable into a top entry, a lens cracked by sun or impact, or a pressure washer. If you’re not sure the rating suits the spot, the IP ratings guide has a location-by-location table.
If there’s water in a mains fitting, switch it off and leave it off. Drying it out might get it working again, but the water has usually started corroding the terminals and driver, and it will be back. Replace it with a fitting rated for the spot, and fit it with the cable coming in from below and a drip loop (a small U-bend in the cable just below the entry) so water drips off rather than running in. Near the sea, materials matter as much as sealing; see outdoor lights for coastal homes.
Sensor lights stuck on or switching randomly
When a light stays on, the wiring is usually fine and the control is the problem. Most PIR lights have three dials: time (how long it stays on), lux (how dark it must be before it works) and sensitivity. If the lux dial has been turned to the sun symbol, it will work in daylight.
On many PIR lights, switching off and on quickly at the wall switch puts them into a manual override that keeps them on. Switch off, wait a minute, and switch back on to reset it. A photocell (dusk sensor) that’s dirty, or newly shaded by a plant or trellis, thinks it’s night. Clean it, clear it, and if it still stays on in full daylight, the sensor has failed.
A light that comes on by itself is usually seeing something: branches moving in the wind, cars or people on the pavement, cats, or warm air from a boiler flue or extractor vent. Turn the sensitivity down, tilt the sensor towards the ground you actually want covered, and use the lens masks if the light came with them. If the light is simply in the wrong spot, where to fit a security light and its PIR sensor covers mounting height and aiming. If it triggers at the same time every night, look for a timer or smart routine instead. Timers also lose their settings after a power cut and need resetting when the clocks change.
Flickering, dim or glowing when off
If one light flickers, try a good-brand LED bulb first, and check the bulb is screwed or pushed fully home. If several flicker together, the problem is upstream: a shared junction box, a loose connection or the supply to that group.
An integrated LED fitting that flickers, cuts out and comes back, or gets dimmer over weeks usually has a failing driver. In many outdoor fittings the driver isn’t sold separately, so it means a new fitting.
LEDs that glow faintly or flicker when they should be off are usually on an electronic PIR, timer or smart switch that lets a tiny current through. Old controls designed for halogen bulbs often do this. The fix is a control rated for LED loads; the same compatibility issue is explained in fixing LED flicker and buzz.
Bulbs keep failing
The most common cause in a sealed lantern or bulkhead is an LED bulb that isn’t rated for enclosed fittings. Heat builds up inside with nowhere to go, and the bulb’s electronics cook. Check the packaging says it’s suitable for enclosed luminaires. Cheap bulbs, a worn lampholder or a loose connection can also kill bulbs early. If a fitting keeps eating good bulbs, replacing the fitting is usually cheaper than the bulbs.
Low-voltage and solar lights
On a 12 V plug-in system, the fault pattern tells you a lot, and with the transformer unplugged it’s safe to work on. If the whole run is out, check the outdoor socket, its RCD and the transformer, including any timer or dusk setting on it. If one light is out, it’s usually the connector for that light: corroded, loose or not pushed fully onto the cable. If the far lights are dimmer, there’s too much cable or too many lights for the transformer.
Solar lights fail for simple reasons. The panel needs direct sun, not the shade of a tree or the eaves, and a wipe now and then. In a British winter there often isn’t enough daylight to charge them fully, so short running times from November to February are normal. I’ve covered solar garden lights that still work in a UK winter separately. Check for an on/off switch or pull tab underneath. The rechargeable battery often only lasts a couple of years; replace it with the same size and type, usually NiMH, never ordinary alkaline batteries. If they’re still poor after that, wire-free path lighting compares better options.
Underground cable faults
A buried cable damaged by a spade, a fence post or rodents gives intermittent tripping, often after rain, and sometimes only some lights working. Problems that start soon after gardening or landscaping point straight at it.
This is electrician territory. Finding the damage takes test equipment, and the repair needs a proper resin-filled joint or a new length of cable. Don’t dig around a live cable to look for it. Buried cable should be suitable for outdoor use and laid deep enough to keep it clear of garden tools; NICEIC’s guide to garden electrics covers what a good installation looks like.
Repair or replace?
Replace the fitting when water has got in, there’s corrosion inside, the housing or lens is cracked, the integrated LED or driver has failed with no spares available, or the IP rating is wrong for where it is. Repair makes sense when it’s a bulb, a sensor setting, a timer, or a loose gland on an otherwise sound fitting.
Swapping a failed outdoor light for a new one on the same wiring isn’t notifiable building work, but it’s still electrical work, so if you’re not confident isolating, connecting and testing it, use a registered electrician. A new outdoor circuit is notifiable under Part P in England, and a registered electrician can self-certify it.
Stopping it happening again
Most repeat faults are designed in. Choose IP65 for anything in the open and IP67 for anything in the ground or a deck. Bring cables into wall lights from below, use glands that match the cable, and keep joints out of the ground: in an accessible outdoor junction box above soil level, or a resin- or gel-filled joint where they have to be buried. Put drivers and transformers somewhere dry and reachable, not buried in a flower bed. For decks in particular, keep connectors off the ground under the boards; the deck lighting guide has more.
When to call an electrician
- The RCD trips again after one reset, or won’t reset at all.
- There’s water inside a junction box, or behind a fitting where the fixed wiring is.
- You see scorching or melting, or smell burning.
- You suspect a damaged buried cable.
- You don’t know which circuit feeds the lights.
- The fix means disconnecting fixed wiring and you can’t safely isolate and test it.
What I'd buy
Affiliate linksFAQs
Why do my outdoor lights trip the electrics when it rains?
Water is getting into a fitting, a junction box or a damaged cable and leaking current to earth, which the RCD detects. Reset it once, then check the lowest fittings with the power off. If it keeps tripping, call an electrician.
Can I fix outdoor lights myself?
You can change bulbs, clean sensors, reset settings and look for water and damage with the power off. Fixed wiring faults, repeated tripping and buried cables are for an electrician.
Is condensation inside an outdoor light normal?
A light mist that clears once the light warms up is normal. Droplets that stay, pooling water or rust mean water is getting in.
Why won’t my PIR light turn off?
Usually the lux dial is set too high, the light is in manual override, or the sensor is dirty or seeing movement. Switch off for a minute to reset it, clean the lens and check the dials.
Why do my solar lights stop working in winter?
Short days and low sun mean the battery doesn’t fully charge. Move them into direct sun, clean the panel and replace old batteries. Some dimming in midwinter is normal.
Do I need an electrician to replace an outdoor light?
Swapping a light on existing wiring isn’t notifiable, but it is electrical work. If you can’t safely isolate, connect and test it, use a registered electrician. A new circuit needs one.
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