How much does a spark plug replacement cost in the UK?

Spark plug replacement costs by engine type

These ranges include a full set of plugs and labour. Prices assume standard access. Restricted access (for example, plugs located under an intake manifold) can add to the labour charge.

Approximate UK market averages as of 2025 at independent garages unless stated. Always get a current quote for your specific engine and model variant.

Spark plug replacement costs by UK city

These ranges reflect a typical full set replacement on a 4-cylinder petrol engine at an independent garage. London and the South East tend to attract higher labour rates.

How often do spark plugs need replacing?

Replacement intervals vary by plug type. Check your vehicle handbook for the manufacturer-specified interval, as this takes precedence over general guidance.

Standard copper plugs

Every 20,000 to 30,000 miles. Standard plugs wear relatively quickly and are fitted as original equipment on older engines. If your car uses copper plugs, check the condition at each major service.

Iridium or platinum long-life plugs

Every 60,000 to 100,000 miles. Long-life plugs use harder electrode materials and maintain a consistent spark gap for far longer. Most modern engines specify this type. Do not replace them early just because the car is being serviced: wait until the mileage interval is reached or a fault is detected.

Manufacturer-specified interval

Some manufacturers link spark plug replacement to a specific major service interval rather than a standalone mileage figure. The handbook or a dealer service schedule lookup will confirm the correct interval for your make and model. Sticking to the manufacturer interval protects the engine and keeps the service history complete for resale purposes.

What affects the cost of a spark plug replacement?

Number of cylinders

A 4-cylinder engine has four plugs; a 6-cylinder has six; an 8-cylinder has eight. Each additional plug adds to both the parts cost and the labour time. Twin-plug engines, which use two plugs per cylinder to improve combustion efficiency, require twice the number of plugs of a conventional engine.

Plug specification

Iridium and platinum plugs cost more per unit than standard copper plugs. On a 4-cylinder engine, the difference in parts cost between a standard set and a long-life iridium set is typically £20 to £60. The labour cost is the same regardless of plug type.

Access and engine layout

On many modern engines, the spark plugs sit in recessed tubes beneath the coil-on-plug ignition units. These are straightforward to access. On some engines, plugs are positioned under or behind intake manifolds, requiring additional strip-down time. V-configuration engines with plugs on both sides of the block also take longer than a straight-4 layout.

Independent garage versus franchised dealer

Franchised dealers charge higher labour rates, typically £90 to £150 per hour compared to £55 to £90 at an independent. On a 45-minute plug replacement, this can mean a £30 to £50 difference in labour alone, on top of any difference in parts pricing. An independent specialist using the correct plugs delivers the same result.

Common questions about spark plug replacement costs

What are the signs that my spark plugs need replacing?

The most common signs of worn spark plugs are engine misfiring (a stuttering or juddering sensation under acceleration), a rough idle that causes the car to shake or vibrate when stationary, poor fuel economy that has worsened noticeably over recent months, and difficulty starting the engine, particularly in cold weather. You may also notice the engine hesitating when you press the accelerator, or the check engine light illuminating. Any combination of these symptoms warrants a plug inspection.

Can worn spark plugs damage the engine?

Yes. A misfiring cylinder caused by a failing spark plug sends unburnt fuel into the exhaust system. This unburnt fuel ignites inside the catalytic converter, causing it to overheat and sustain internal damage. Catalytic converter replacement is an expensive repair, typically costing £300 to £900 or more depending on the car. Persistent misfires can also foul the oxygen sensors and, in severe cases, cause carbon deposits to build up on the piston and cylinder head. Replacing plugs at the correct interval is one of the most cost-effective ways to protect the exhaust and emissions system.

Can I replace spark plugs myself?

On many petrol engines, spark plug replacement is a straightforward job that a competent DIYer can complete with basic tools. You will need the correct socket size (typically 16 mm or 21 mm), a torque wrench, and the right plugs for your engine specification. The critical step is torquing the plugs to the manufacturer's specification: over-tightening can strip the thread in the cylinder head, which is a costly repair. On some modern engines, particularly those with coil-on-plug ignition systems or direct injection, access can be restricted and the job may be better left to a garage. Always disconnect the battery and allow the engine to cool fully before starting.

What is the difference between standard and iridium spark plugs?

Standard copper-core spark plugs are the least expensive option, typically costing £3 to £8 each, but they have the shortest service life, generally 20,000 to 30,000 miles. Iridium and platinum long-life plugs use harder electrode materials that resist wear, giving a service life of 60,000 to 100,000 miles. They cost more per plug (£10 to £25 each), but over the life of the vehicle the total cost is comparable, and they require fewer replacement intervals. Many modern engines specify iridium or platinum plugs as standard. Always fit the grade the manufacturer recommends, as fitting a lower-specification plug than required can cause misfires.

How long does a spark plug replacement take?

On most 4-cylinder engines with easy access, a mechanic can replace all four spark plugs in 30 to 45 minutes. On 6-cylinder or V-configuration engines, or where the plugs are in a restricted location (such as under an intake manifold), the job can take 60 to 90 minutes or longer. Twin-plug engines, which have two plugs per cylinder, take roughly twice as long as a standard 4-cylinder. Labour time is the main driver of cost variation between jobs.

Should I replace all spark plugs at the same time?

Yes. Spark plugs in the same engine wear at approximately the same rate because they experience the same operating conditions and mileage. Replacing only the plug that has visibly failed leaves the remaining plugs at the same stage of wear, meaning they are likely to fail shortly afterwards. Replacing the full set in one visit saves repeated labour costs and ensures all cylinders fire consistently. The cost difference between replacing one plug and all four is usually small when labour is already being charged.

Does a car service include spark plug replacement?

It depends on the service type and the mileage interval. A minor or interim service does not typically include spark plug replacement. A major or full service may include plugs if the car has reached the manufacturer's recommended replacement mileage, which varies by plug type (see intervals below). Many manufacturers specify plug replacement as part of a scheduled service at a particular mileage rather than a fixed annual interval. When booking a service, ask whether the service schedule includes spark plug replacement for your car's current mileage.

What happens if you ignore worn spark plugs?

Ignoring worn spark plugs leads to progressively worse running. The engine will idle roughly and may misfire under load. Fuel economy will decline as the engine management system struggles to compensate for incomplete combustion. Unburnt fuel entering the exhaust will damage the catalytic converter over time, potentially leading to an emissions-related MOT failure. A car with a misfiring engine will fail the MOT emissions test. In a prolonged misfire, the catalytic converter can sustain irreversible damage, turning a modest plug replacement cost into a significantly larger repair bill.