Slow puncture: signs, causes, fixes and the MOT

A slow puncture is a leak that lets a tyre lose air gradually, over hours, days or even weeks, instead of going flat at once. It is usually a nail or screw in the tread, a leaking valve or a poor seal between the tyre and the wheel rim. Which fix it needs is only certain once the tyre is taken off the wheel and checked from the inside.

The catch is that it never forces you to stop. You top it up, it holds for a few days, and meanwhile the tyre runs soft, wears its edges and heats up every time you drive. Below: how to tell a slow puncture from cold weather and how to find where the air is going. Then what each cause needs, whether you can drive on it, and what it means for your MOT.

What is a slow puncture?

TyreSafe, the UK tyre safety charity, defines it simply as a puncture that releases air from your tyre very slowly. It notes that one may take days or weeks to become obvious (TyreSafe). There is not always a hole. The air can just as easily be escaping past the valve or around the bead, the edge of the tyre that seals against the wheel rim. That is why some slow punctures are found only once a fitter looks for them.

How fast the tyre drops varies. If it is soft every morning after a night parked, the leak is fairly quick; a few psi lost over a week is a very slow one. The rate tells you how urgent it is, but on its own it does not reliably tell you the cause.

Signs of a slow puncture

• One tyre always needs air. Topping up the same corner while the other three hold is the clearest sign there is.
• The warning light keeps coming back. On a car with a tyre pressure monitoring system (TPMS), the TPMS warning light goes out once you inflate the tyre, then returns a few days later. TyreSafe notes that in many cases the warning light resets once the correct pressure is restored (TyreSafe TPMS). So a light that keeps returning points to air going somewhere.
• The car pulls or feels different. TyreSafe lists drifting to one side, a shudder through the steering wheel, and steering or cornering that feels different (TyreSafe).
• A faint hiss or ticking. Also on TyreSafe's list of signs.
• It looks low after standing. Compare the bulge at the bottom of the tyre with the one on the other side of the same axle first thing in the morning.
• The edges wear first. Prolonged under-inflation wears the outer edges of the tread fast (TyreSafe).

Slow puncture or just cold weather?

Air contracts as the temperature falls, so on a cold morning all four tyres read lower. Toyota notes it is not uncommon for the warning light to come on in colder weather, especially if pressures were already near the minimum (Toyota UK). The test is consistency. Cold affects all four tyres roughly equally; a slow puncture keeps draining the same tyre whatever the weather.

So check all four, cold, before you drive, as TyreSafe advises (TyreSafe TPMS). Set them to the pressure on the sticker in the door shut or fuel flap and check again in two or three days. If one is clearly lower than the rest, it is a leak.

What causes a slow puncture, and how each is fixed

Nails, screws and other sharp objects

TyreSafe says that most of the time a slow puncture comes from sharp objects such as glass or nails piercing the tyre (TyreSafe). The object often plugs its own hole, which is why the leak is slow. Leave it in until the tyre is off the wheel. Our guide to a nail or screw in the tyre explains why pulling it out at the kerb usually turns a slow leak into a flat.

Valve caps, cores and valves

The cheapest fix comes first. TyreSafe says a missing or poorly sealing cap can let air out (TyreSafe), and Michelin says a valve must always have a cap (Michelin). Beyond that, the rubber in a snap-in valve loses its sealing properties with age, and the core inside can leak. Michelin adds that valve porosity is not common but does happen. A valve replacement is a small job compared with the tyre a leaking valve slowly ruins.

Valves on cars with TPMS sensors

On many cars with direct TPMS, the valve is part of the sensor: a TPMS sensor valve. If it leaks, Michelin says the whole valve is not replaced, only the seal inside (Michelin). TyreSafe says it must never be swapped for a standard non-TPMS valve (TyreSafe TPMS). If the sensor itself has failed, that is a TPMS sensor replacement.

Rim corrosion

Michelin lists an old, rusty rim among the reasons a tyre loses pressure faster than it should (Michelin). Kwik Fit, a tyre retailer, says corrosion can open gaps between tyre and rim. The RAC, a motoring organisation that also fits tyres, lists corroded wheels as a cause too (Kwik Fit, RAC). The MOT angle is narrower: the DVSA MOT manual records a tyre incorrectly seated on the wheel rim as a major defect. The usual trade fix is to take the tyre off, clean the bead seat back to sound metal and refit the tyre with bead sealer. Where the corrosion is deep, the wheel needs a refurbishment specialist before it will hold air reliably; we do not refurbish wheels.

Cracked or bent wheels

A hard pothole or kerb strike can crack an alloy. The DVSA MOT manual treats any fracture on a wheel as a dangerous defect. Where the crack sits is trade experience. The Wheel Specialist, a wheel repair business, says it is often on the inner barrel close to the bead seat. There you cannot see it with the wheel on the car (The Wheel Specialist). No tyre work cures a cracked wheel. Some cracks can be welded by a wheel specialist; others mean a new wheel.

Tyre keeps going flat but there is no puncture?

Then the air is usually leaving at the valve or the rim, or through a hole too small to spot. Michelin says a tyre that is flat without being punctured or damaged may have a leaking valve or wheel (Michelin). Work through it in this order:

1. Valve cap. Is there one, and is it screwed on? If not, fit one and see if the loss stops.
2. Soapy water test. Inflate the tyre to the right pressure. Then brush or spray soapy water over the valve, wiggling it gently as Michelin suggests. Do the same all round the joint between tyre and rim on the outer face, and across the tread. A cluster of small bubbles that keeps growing marks the leak.
3. The inner face. You usually cannot reach the inside of the rim with the wheel on the car, so no bubbles on the outside does not mean no leak.
4. Off the wheel. If nothing shows, the tyre needs to come off so the inside of the tyre, the bead seat and the wheel barrel can be checked. That is where cracks and corrosion hide.

How do I fix a slow puncture?

You find it, then have it repaired properly with the tyre off the wheel. A top-up or a can of sealant only buys time.

1. Check the cap and find the leak. With the tyre inflated, brush soapy water over the valve, the rim edge and the tread, and look for bubbles that keep growing.
2. Leave any object in place and keep journeys short until the tyre is seen.
3. Have the tyre removed and inspected inside. TyreSafe says permanent repairs can only be done once the tyre is off the wheel and inspected inside and out. They are done by a tyre specialist, to BS AU 159 (TyreSafe).
4. Repair the right thing. A tread puncture gets a rubber combination plug-patch, or a patch plus filler, fitted from inside (BTMA). A valve leak gets a new valve or seal; a rim leak gets the bead seat dealt with. Then the tyre is refitted, inflated and the wheel balanced.

Already used sealant or a string plug? The British Tyre Manufacturers' Association does not recognise liquid sealants or plugs pushed in from outside as repairs (BTMA). TyreSafe calls emergency kits a short-term measure only (TyreSafe).

Sealant does not automatically mean a new tyre. Goodyear notes the inside can be cleaned and repaired, though some fitters will not do it because it is messy (Goodyear). Tell the fitter before they arrive.

Can a slow puncture be repaired?

Yes, if the hole is in the central part of the tread and no more than 6mm across, and the tyre turns out to be sound inside. No source we found says what share of slow punctures that covers, so we do not give one. A leak at the valve or the rim does not involve repairing the tyre at all. For the tyre itself, the BTMA's summary of BS AU 159 sets the limits (BTMA):

• Where: only in the central repair zone the standard calls area T, which is 60, 65 or 70 percent of the tyre's width depending on its size. Nothing in the shoulder or sidewall.
• How big: up to 6mm across on a car tyre, measured after the hole has been prepared.
• How: the tyre off the wheel, inspected inside and out, and repaired from inside.
• Earlier repairs: there is no limit on the number of repairs in area T as long as the patches do not overlap.

What rules a repair out is damage found on inspection: tread below the legal 1.6mm, bead or inner liner damage, or damage from running under-inflated or flat. Michelin explains that driving at low pressure crushes the sidewall and marks the inside of the tyre. It adds that a damaged carcass cannot be repaired, even if the hole is in the tread (Michelin). Done properly, the BTMA says a repaired tyre can run at its original speed and load ratings. The full rules, including how run-flats differ, are in can a puncture be repaired?

Can you drive with a slow puncture, and for how long?

Only gently and only as far as getting it fixed. There is no safe number of miles, because it depends entirely on how fast the tyre is losing air. TyreSafe says that in some cases you may be able to drive a short distance on a punctured tyre. It adds that this means low speed only and for the minimum distance needed to reach a garage or safe place (TyreSafe).

It is also a legal point. The Highway Code says tyres must be correctly inflated to the vehicle maker's specification for the load being carried (Highway Code, Annex 6). So if you must use the car before it is fixed:

• Check the pressure cold before every journey and inflate to the door sticker figure.
• Keep trips short and speeds down; avoid motorways, long runs and heavy loads.
• If it is visibly soft again by the next morning, stop using it and have it seen where it is parked.
• Get it repaired within days, not weeks.

If the tyre has already gone fully flat, the rules change: see is it safe to drive on a flat tyre?

Can a slow puncture cause a blowout?

Yes, if it is ignored. TyreSafe warns that prolonged under-inflation causes excessive flexing and a build-up of heat, making a dangerous blowout much more likely (TyreSafe). Speed, distance and load all add heat. If a tyre does fail at speed, here is what to do in a blowout.

Running soft for weeks can also damage the tyre inside, which can turn a repairable hole into a new tyre. See why running soft can rule out a repair.

Will a slow puncture fail an MOT?

Not on its own, but what it causes can. The DVSA MOT inspection manual records these items:

• Tyre obviously under-inflated: minor defect. It goes on the certificate but does not fail the test.
• Tyre pressure monitoring system malfunctioning or obviously not working: major defect, a fail. This is checked on passenger cars first used on or after 1 January 2012.
• Warning lamp on because a tyre is low: not a fail on its own. The manual says this does not automatically mean the system has a malfunction. If the tester cannot tell which it is, they add an advisory.
• Tyre valve seriously damaged or misaligned, likely to cause sudden deflation: dangerous defect.
• Tyre incorrectly seated on the rim: major defect.

So a slow puncture usually costs you an advisory or a minor, not a fail. Do not rely on that. Fix the leak and get the warning light out before the test, so nobody has to judge whether the system is faulty.

How much does it cost to fix a slow puncture?

It depends on the cause. A tread repair, a new valve, a seal kit for a TPMS sensor valve and a rim reseal are different jobs. A tyre that turns out to be unrepairable needs replacing. Catching it early keeps it at the smaller end, because a tyre run soft for weeks can end up unrepairable even though the hole was small. Ask us on the phone. Nights, weekends and bank holidays cost the same as weekdays, with no out-of-hours surcharge.

What a fitter checks when they get to the car

This is how the job normally runs, so you know what you are paying for and why a repair sometimes becomes a new tyre:

1. Pressures on all four tyres, to confirm which one is leaking and how fast.
2. The valve cap, core and valve body, with soapy water.
3. The tread and both sidewalls, looking for the object, cuts and bulges.
4. The wheel comes off and the tyre comes off the wheel. The inside of the tyre is checked for crush marks or mottling that mean it was run too soft.
5. The hole is measured and its position checked against area T, and any earlier repair is checked for overlap.
6. The bead seat and inner barrel of the wheel are checked for corrosion and cracks.
7. Repair or replace, refit, inflate to the door sticker figure and balance the wheel.

Slow puncture repair near me: we come to the car

A slow puncture is the ideal job to have done where the car is parked. The car can usually still be moved onto the drive or into a work car park first. Our slow puncture repair service is mobile. A fitter comes to your home or work, 24/7, finds where the air is going and fixes tread and valve leaks on the spot. Tread punctures are repaired to BS AU 159 where the damage allows. If the tyre cannot be repaired, a new one can be fitted the same day. We typically arrive within 30 to 60 minutes across London and the surrounding counties. The fitting itself takes 20 to 30 minutes, and the wheel is balanced on the van.

We do not repair wheels. If the leak turns out to be a cracked or badly corroded wheel, we will tell you plainly and point you to a wheel specialist. Searching for a tyre repair near you? That page shows the areas we cover.

What to tell us when you ring:

• Where the car is, and whether it is on a drive, a street or a car park.
• Which tyre, and how fast it is dropping (every morning, or every week).
• Whether the warning light is on, and whether you have used sealant or a plug.
• The tyre size from the sidewall, for example 205/55 R16 91V, in case it needs replacing.
• Whether the car has locking wheel nuts, and where the key is.

If the tyre has gone fully flat or you are stuck at the roadside, use our 24/7 emergency tyre call-out. On a motorway, never wait for any repair on the hard shoulder. Get out on the side away from the traffic, wait behind the barrier and ring 999 or National Highways on 0300 123 5000. We fit once the car is off the motorway.

Sources

Checked on 2 October 2026. Some points are trade practice or retailer advice, not a published standard. They are how a repair is done, what a fitter checks, how a corroded bead seat is cleaned and where wheel cracks usually show up. They are written that way. Fast Tyre service details are as confirmed by the business.

• British Tyre Manufacturers' Association, Minor repairs to passenger car and light van tyres (PDF, issued 2010, reviewed 2014. It quotes BS AU 159f; the current edition is G, and the full standard is a paid BSI document)
• DVSA, MOT inspection manual, section 5: axles, wheels, tyres and suspension
• GOV.UK, The Highway Code, Annex 6: vehicle maintenance, safety and security
• TyreSafe, Punctures and puncture repairs, Tyre safety, Tyre pressure monitoring system and Emergency puncture repair kits
• Michelin UK, How to replace a tyre valve, Tyre repair: is my tyre repairable?, How and when to check your tyre pressure and What to do with a flat tyre
• Goodyear, Spare tyres vs repair kits
• RAC, What is a slow tyre puncture? and Kwik Fit, Spotting the signs of a slow puncture (a motoring organisation that also fits tyres, and a tyre retailer; used only alongside the sources above)
• The Wheel Specialist, Cracked alloy wheel repair (a wheel repair business)
• Toyota UK Magazine, Tyre pressure warning light

How this guide was checked: written by Abed Jabbarkhel, founder of Fast Tyre and a director of Fast Tyres Ltd since April 2021 (Companies House). His vans repair punctures and replace valves at the car. Every outside fact above is linked to its source. Where no source gives a figure, such as how many slow punctures come from valves, we do not give one. Spotted something out of date? Tell us through our contact page. The flow chart is Fast Tyre's own. Photo: Andrea Piacquadio on Pexels, taken in a workshop rather than on one of our jobs.

Frequently asked questions