A valve has several parts: the stem fitted through the wheel, the core that opens and closes to let air in, and the cap that keeps dirt out. On cars with TPMS sensors, the valve is also part of the sensor assembly, so it needs more care.
Signs your valve may be at fault
- A tyre loses pressure steadily with no sign of a nail or cut.
- The tyre goes down more after the car sits in cold weather.
- You can hear a faint hiss when you remove the valve cap.
- The valve stem looks cracked, perished or leans at an odd angle.
- The cap is missing or the core is loose.
- Corrosion is visible around the base of the valve on an alloy wheel.
How to test a valve
- Make sure the tyre is inflated to a reasonable pressure.
- Mix a little washing-up liquid with water and brush it over the valve end, the cap and the base where the stem meets the wheel.
- Watch for bubbles. A stream of bubbles from the core means the core is leaking. Bubbles at the base mean the stem seal has failed.
- Check the rest of the tyre in the same way, especially the bead area where the tyre meets the rim.
If the valve is the culprit, tighten a loose core with a valve core tool or replace it. A rubber stem that has perished needs replacing with a new one, which means the tyre has to be removed from the wheel.
Why valves fail
Rubber valve stems perish with age, heat and road salt. Valve cores wear from repeated use and from dirt caught when the cap is missing. On alloy wheels, corrosion between the stem and the wheel can cause a slow leak. It is why many fitters replace valve stems whenever new tyres are fitted, which is inexpensive insurance against slow leaks later.
Also see slow puncture signs for other causes of pressure loss.
TPMS valves
On a car with direct tyre pressure sensors, the valve forms part of the sensor. Seals, nuts and cores may need replacing when the tyre is changed, and the sensors can corrode if the seal fails. If your warning light is on and the valve is leaking, read TPMS light on and see our TPMS and valve replacement service.
Fixing it on site
A mobile technician can replace a valve core or stem at your location. For a stem replacement, the tyre is broken from the rim, the old stem removed, a new one fitted, and the tyre inflated and checked for leaks. If the wheel is also corroded at the bead, the area can be cleaned and sealed. Learn how the visit works in our mobile fitting guide, or look at mobile tyre repair and puncture repair.
We attend homes and workplaces in places such as London, Reading, Leeds and Birmingham. See the areas list. Call now for a quote on 0800 772 0355 or book now.
Simple valve care
- Always fit a valve cap; it seals out dirt and moisture.
- Use metal caps only if they are the right type, as some can seize on aluminium stems.
- Do not overtighten caps.
- Have valves checked whenever tyres are changed.
- If you use a tyre inflator, press the connector on squarely to avoid bending the stem.
Why a repeat inspection matters
If the tyre continues to lose air after the valve has been replaced, there may be a second source of leak: a bead seal, a corroded rim or a small puncture. Good fitters test the whole assembly in water or with soapy solution before the job is finished, and it is worth asking them to do so.
Valve caps, cores and the cold-weather effect
A leaking core often only shows itself in cold weather, because the rubber seat inside contracts and lets a little air creep past. Drivers sometimes notice the pressure warning on frosty mornings that clears once the tyre warms up, then returns a few days later. That pattern points at a valve or bead seal rather than a nail, and a quick soapy-water test usually settles it.
Missing caps matter more than most people think. The cap is a secondary seal, and without it grit and moisture reach the core and speed up wear. Keep a couple of spare plastic caps in the glovebox. Replace any cap that is cracked or has lost its internal sealing ring, and never drive with an uncapped valve for long.
Frequently Asked Questions
Can a valve leak cause a flat tyre?
Yes. A faulty core or stem can lose air steadily until the tyre is flat.
How do I check my valve?
Brush soapy water over the valve and watch for bubbles.
Can a valve core be replaced without removing the tyre?
Often yes, using a core tool, but a failed stem needs the tyre removed.
Can you replace it at my home?
Yes, in most cases. Call now for a quote on 0800 772 0355.
Related Help
Need help with your tyres now?
Call now for a quote, or book now online. Phone 0800 772 0355.