You topped up the same tyre last week. And the week before. And the one before that. The other three are fine.
You have looked for a nail or screw and found nothing. The tyre looks normal. But the pressure keeps dropping.
This is one of the most common tyre problems UK drivers deal with. The cause is almost always one of about eight specific things, and most of them you can either diagnose yourself or have a mobile fitter sort on your driveway.
Short version: a tyre that keeps losing air usually has an embedded object you cannot see, a faulty valve, a corroded wheel rim, or a slow bead-seat leak from old kerb damage. Here is how to find the cause and decide between a repair and a replacement.
How fast is the leak? The pressure-loss diagnostic
This is the single most useful thing to know, and almost no driver does. The rate of pressure loss tells you what kind of leak you are chasing.
| Pressure loss rate | Most likely cause | Action |
| 1 to 3 PSI per month | Normal osmosis, air slowly passing through rubber | Top up monthly, no fault |
| 1 to 2 PSI per 10 degree cold drop | Temperature, not a leak | Top up to spec when cold |
| 1 to 3 PSI per day | A small puncture or valve issue | Investigate within days |
| 4 to 6 PSI per day | A significant puncture or bead/valve leak | Inspect within 24 hours |
| 5+ PSI overnight when parked | A real leak at the bead, rim, or valve | Get the tyre removed and inspected |
| Visibly down in minutes | An active puncture or blowout starting | Pull over now and call us |
To measure it, check the pressure twice, 24 hours apart, both readings taken cold. The difference is your leak rate, and the number is effectively the diagnosis.
Not sure of your rate? Top up, leave it 24 hours, recheck, then WhatsApp the numbers to wa.me/447955533000 and we will tell you what it points to.
Quick answer: what to do this week
- Top up to spec when cold, and note the exact pressure.
- Recheck 24 hours later, also cold. The difference is your leak rate.
- Walk around the tyre, checking the tread, sidewall, and wheel edge for damage or objects.
- Do the soapy-water test below, since most leaks show within five minutes.
- Mark any leak you find with chalk or tape.
- Call us to diagnose and repair or replace at your driveway or work.
- Do not top up forever. Slow leaks tend to get faster, not slower.
The 8 most common causes of a slow leak
Here is what we actually find when we take these tyres off.
1. An embedded object in the tread, the most common
A nail, screw, or sharp stone can partly seal its own hole, which is why you keep losing air slowly. Pulling it out without preparing to re-inflate makes things worse. Best practice is to leave it in and call for inspection. Our guide to a nail or screw in a tyre covers this in full.
2. A faulty valve core
The valve core is the tiny spring-loaded part inside the valve that holds air in. It often leaks after being over-tightened at a service, or when grit gets in the seal. Fix: a new valve core, usually a few pounds plus labour.
3. A faulty or damaged valve stem
The stem that pokes through the wheel can crack with age, especially on cars over eight years old. Aluminium TPMS valve stems can corrode where they meet the wheel. Fix: a replacement stem during tyre removal, typically £15 to £30.
4. Bead-seat corrosion, often from an old kerb hit
Damage to the alloy edge where it seals against the tyre lets air past as it corrodes. This is the classic delayed leak, a kerb scuff from months ago surfacing now. Our guide to kerbed wheels explains the cause. Fix: clean the bead seat and re-seal, typically £30 to £50.
5. A bent or buckled rim, often from a pothole
A hard pothole impact can deform the wheel edge, sometimes invisibly until the tyre is off. Our guide to pothole damage covers this. Fix: wheel straightening at £40 to £100 if minor, or replacement if major.
6. A cracked alloy
A hairline fracture can be invisible even on the wheel surface, and is common on old, heavily used alloys. Some are weldable by a specialist, structural cracks are not. Fix: confirmed by a tyre-off inspection, then weld or replace.
7. Tyre porosity from age
Old tyres develop tiny cracks across the sidewall, especially on cars that sit unused, and the micro-leaks add up. Our guide to tyres cracking with age covers this. Fix: replacement.
8. Multiple tiny embedded objects
Several small pins or slivers across the tread can each leak gently, and soapy water may find none of them. This often happens after driving over scattered debris near construction or farm yards. Fix: usually replacement.
How to find the leak yourself: the soapy-water method
The soapy-water test costs about £1.50 and twenty minutes. We will walk you through it, because if you find the leak in the tread you might not even need us, and if you find nothing, that is useful too.
You need: a spray bottle of soapy water (one part washing-up liquid to about four parts water), a working pressure gauge, and a bit of patience.
- Inflate the tyre to spec, or a few PSI higher for testing.
- Spray generously over the whole tyre, the tread, sidewall, valve, and where the tyre meets the wheel.
- Wait 3 to 5 minutes. Do not rush, since slow leaks bubble slowly.
- Watch for a growing single bubble (a clear leak point), a foamy patch (multiple micro-leaks), or bubbles at the valve (a valve fault).
- Mark the spot with chalk or tape before the water dries.
- If nothing shows on the tread, focus on the bead, where the tyre seals against the wheel. That is where most invisible leaks hide.
When soapy water will not find it
- Very slow leaks under 1 PSI a day can take longer than five minutes to show
- Bead-seat leaks often hide behind the wheel lip
- Multiple micro-punctures show as nothing in particular
- Internal damage from driving on a flat will not show with external water
- Cracked alloys can leak only under the car’s weight
If you find nothing, the leak is almost certainly at the bead or inside the tyre, and that needs the tyre off the wheel.
Repair, replace, or live with it? An honest decision
Likely repairable
- A single puncture in the central tread area
- A hole under 6mm, about a match head
- No previous repair in the same spot
- Tyre otherwise in good shape, tread above 3mm
- Not driven on while flat
UK repairs are governed by the BSAU 159 standard, which means a proper plug-and-patch from inside the tyre, not a rope plug pushed in from outside. A proper repair typically costs £25 to £45.
Not repairable, needs replacing
- Any sidewall or shoulder damage
- A hole larger than 6mm, or several holes close together
- Tread below the 1.6mm legal minimum
- Visible cords or belt damage
- A tyre run flat for any real distance
Wheel issues
Bead-seat corrosion is a clean-and-reseal at £30 to £50. A minor bent rim straightens for £40 to £100. A cracked alloy is welded if non-structural, otherwise replaced. Heavy corrosion means refurbishment at £80 to £150 per wheel.
Why not just keep topping it up
Slow leaks tend to accelerate, so 2 PSI a day becomes 5, then sudden failure. Underinflation also wears the tyre unevenly, so you replace it sooner anyway, and it dents your fuel economy. Worst of all, a leak that fails at speed or in bad weather is a real safety risk.
The real cost of just keeping it topped up
The visible cost feels tiny, free air and a few minutes. The hidden cost is the problem.
Persistent underinflation can shorten a tyre’s life by a quarter to a half through uneven wear, and it quietly costs you fuel. The kicker is the ending: a £40 repair you keep putting off becomes a £200-plus replacement, often with alloy damage too.
A £40 repair now saves a £200 replacement later. A £30 bead-seat reseal saves the whole tyre. Topping up forever is the most expensive option of the lot.
Will a slow puncture fail an MOT?
It can. The tester checks the pressure by eye, the tread depth, and for visible damage, and a noticeably soft tyre can be flagged.
If your TPMS light is on because of the leak, that is an automatic fail on cars registered on or after 1 January 2012, as set out in the DVSA MOT rules. If the underlying damage is to the sidewall or structure, that fails too.
To avoid a needless fail, top up to spec the morning of the test, sort any slow leak at least a week ahead, and allow time for a TPMS relearn if a sensor was involved. Our TPMS guide covers that side of it.
Scotland-specific factors in slow leaks
A few local conditions make slow leaks more common up here.
Winter salt and alloy corrosion. Scottish road salt is heavy from November to March, and it attacks alloy edges and bead seats hard. A wheel that was fine can develop a corrosion leak after a single winter, so cleaning your alloys in winter is not just cosmetic.
Cold-cycle swings. A Glasgow morning at minus 2 from an autumn 10 degrees leaves tyres 2 to 3 PSI down at start-up, which makes a real leak look worse in the cold. Our TPMS guide explains why cold mornings trigger most warnings.
Spring potholes. Scottish potholes peak after the winter freeze-thaw, and a bent rim from a spring pothole often shows up as a slow leak in summer.
Highland debris. Highland and single-track routes pick up farm-vehicle nails and wire faster than urban roads, so slow leaks often appear in the days after a Highland trip.
A real callout pattern we attend most weeks
We do not need to invent this one.
A driver in Pollokshields had been topping up the same front-left tyre weekly for two months. No visible damage, and soapy water showed nothing. They finally called when the leak sped up to 3 PSI overnight.
We took the tyre off the wheel. Inside were three tiny embedded pins, barely visible from outside, plus mild corrosion on the bead seat.
Because the punctures were multiple and close together, the tyre was not safely repairable, so we fitted a matching new one and cleaned and resealed the bead seat for good measure. The whole job took around 40 minutes, and the final cost was less than the driver had feared. The bonus was the fuel and tyre life they stopped wasting on the other three.
Need us nearby? See our pages for Glasgow, Edinburgh, Aberdeen, Dundee, and Inverness.
Frequently asked questions
Why does my tyre keep losing pressure?
The likeliest causes are an embedded object in the tread that is partly sealing its own hole, a faulty valve, a corroded bead seat from forgotten kerb damage, or a bent rim from a pothole. Less common causes are a cracked alloy, tyre porosity from age, or several tiny embedded objects.
How do you find a slow puncture?
Inflate the tyre, spray soapy water over the whole thing, and watch for bubbles over 3 to 5 minutes. The bubbles pinpoint the leak. If nothing shows, it is usually at the bead seat or internal, which needs a professional with the tyre off the wheel.
Can a slow puncture be repaired?
Yes, if it is in the central tread, under 6mm, with no sidewall damage, no previous repair in the same spot, and the tyre has not been run flat. UK BSAU 159 governs what is safe. Sidewall and shoulder damage are never repairable and need replacement.
How much does a slow puncture repair cost in the UK?
A proper plug-and-patch repair is typically £25 to £45. A valve core is £10 to £20, and a bead-seat reseal £30 to £50. If the tyre needs replacing, expect £80 to £220 depending on size and brand. Ask for the diagnosis cost upfront if anything is uncertain.
Is it dangerous to drive with a slow puncture?
Yes, increasingly so as it worsens. Underinflated tyres are more prone to sidewall damage, blowouts, and poor handling in an emergency, and slow leaks tend to accelerate. Get it diagnosed within days rather than months.
How long can I drive on a slow puncture?
Short, low-speed trips to reach a fitter are usually fine if the tyre is holding most of its pressure. Driving daily for weeks while topping up causes uneven wear, wastes fuel, and ends in failure. Treat it within days.
Will a tyre repair kit fix a slow puncture?
A factory sealant kit is for emergency tread punctures under about 4mm only. It does not fix bead-seat leaks, valve faults, or rim damage, which cause most slow leaks. Our guide to a sealant kit that will not work explains why.
Why is my tyre losing pressure but no puncture is visible?
The leak is probably at the bead seat, a faulty valve, a hairline alloy crack, or several tiny objects, none of which show from outside. A mobile fitter can take the tyre off and inspect properly, which is the reliable way to find an invisible leak.
Tired of topping it up? Here’s what to do
You have been patient with this, and that is reasonable. But it will not fix itself.
- Stop ignoring it, slow leaks accelerate
- Call us: 07955 533000, diagnosis at your driveway, no garage queue
- WhatsApp your tyre size and location: wa.me/447955533000
- Repair £25 to £45 or replacement from £80, honest pricing before any work
- Average arrival 30 to 45 minutes across Scotland, 24/7
- We bring a matching tyre if replacement is needed, so it is one visit
If we can repair it rather than replace it, we will tell you. That is the whole point of getting it properly diagnosed.
