How much does a spark plug replacement cost?
A spark plug replacement in the UK typically costs £100 to £250 for a full set fitted on a normal four cylinder petrol car. The RAC puts the average at around £153 and gives manufacturer examples from about £121 on a Toyota to about £186 on an Audi. The plugs themselves are cheap, often £4 to £25 each, so most of what you pay is labour: roughly an hour on an easy engine, and considerably more where the inlet manifold has to come off to reach the back cylinders. Diesel cars have no spark plugs at all, so if you have been quoted for a set on a diesel, ask again.
A spark plug is one of the cheapest parts on a petrol car and one of the most expensive to ignore. Four small pieces of ceramic and metal fire tens of millions of times between services, and when they finally give up they almost never announce themselves as worn plugs. They show up as a misfire, a hesitation on a hill, a car that turns over and over on a cold morning, or an engine light that sends you looking for something far more serious. This guide sets out what a spark plug change actually costs in the UK, when it is genuinely due, and how to tell a £150 job from a £600 one before you agree to anything.
How much does a spark plug replacement cost?
A spark plug replacement in the UK usually costs £100 to £250 for a full set fitted on a normal four cylinder petrol car. The RAC puts the average at around £153 and gives a complete set range of £50 to £250 and above, along with worked manufacturer examples: around £121 on a Toyota, £126 on a Ford, £177 on a BMW and £186 on an Audi.
Read those figures as markers rather than a price list. The spread within a single manufacturer is wider than the gap between two badges, because the number that really moves is how long it takes to reach the plugs on your engine, not whose name is on the bonnet.
| What you are having done | Typical total cost | What drives the price |
|---|---|---|
| Four plugs fitted, easy access | £100 to £180 | Coils lift off the top of the engine, around an hour of labour |
| Four plugs fitted, awkward access | £180 to £250 and above | Inlet manifold or covers have to come off first |
| Six or eight plugs, V engine | Toward the top of the range and beyond | More plugs, and the rear bank is usually buried |
| Plugs added to a booked service | Parts plus a little labour | The car is already in and partly stripped |
| The plugs on their own, over the counter | £4 to £25 each | Copper at the bottom, iridium at the top |
Nothing caps this price the way the law caps an MOT at £54.85. It is set by your garage hourly rate and by your engine design, which is why two quotes on the same street can be £100 apart for what sounds like an identical job.
Does your car even have spark plugs?
This sounds like an odd question to ask in a cost guide, but it is the single most useful thing on this page and it saves real money.
Diesel cars do not have spark plugs. A diesel ignites its fuel by compressing the air until it is hot enough to burn, so there is no spark and nothing to change. What a diesel has instead is a set of glow plugs, which warm the combustion chamber to help the engine start from cold and then take no further part once it is up to temperature. They are a different part, they fail differently, and they are priced differently. If you drive a diesel and someone has quoted you for spark plugs, ask them to say exactly what they are replacing before you say yes. Diesel owners have their own running costs to watch instead, mostly around the DPF and AdBlue.
Fully electric cars do not have them either, because there is no combustion at all. That is one of the reasons an EV service costs less, as how servicing an electric car differs explains. Petrol hybrids do have spark plugs, and they are a genuine service item, though a hybrid that spends a lot of time on the electric motor may reach the mileage interval slowly.
Why the labour, not the plugs, sets the price
The parts on this job are cheap. A copper plug can be a few pounds and a long life iridium plug for a modern turbocharged engine is usually £15 to £25. Four of those is rarely more than £100 even at the top end, and often far less. Everything above that number on your bill is time.
At typical UK workshop rates of £60 to £100 an hour, the difference between a one hour job and a three hour job is most of the difference between a £130 bill and a £300 one. What decides which one you get is access:
- Coil on plug, straight down the top. The best case. Undo a bolt, lift the coil, wind the old plug out, torque the new one in. Four cylinders in about an hour.
- Covers and pipework in the way. An engine cover, an air intake pipe and a wiring loom to move before you can start. Adds half an hour or so.
- Inlet manifold off. Common on V6 engines where the rear bank of plugs sits under the manifold. This turns a simple job into a strip down with gaskets to replace, and it is the main reason some quotes look startling.
- Plugs stuck or seized. On a car that has gone a long way past its interval, plugs can seize into an aluminium head. Freeing them carefully takes time, and getting one wrong means a stripped thread and a much bigger repair.
The practical move is to ask the garage, when you request the quote, how many hours they have allowed and why. A garage that answers that specifically for your registration is one worth using. Our guide to questions to ask a garage before you book has the rest of the list.
How many plugs does your car have?
The RAC notes that most vehicles have four spark plugs, with V6 engines typically using six, V8 engines eight and rotary engines three arranged in a triangular unit. They are always replaced as a complete set. Changing one and leaving three old ones gives you an engine running on mismatched components, and you will be paying the same labour again shortly.
How often should spark plugs be changed?
There is no single answer, and any guide that gives you one is guessing. The RAC puts the full range at every 20,000 to 150,000 miles depending on the quality of the plugs and how often the car is serviced. Protyre narrows the common case to every 30,000 to 90,000 miles.
The variable that explains that enormous spread is what the plugs are made of.
Copper, platinum and iridium
Carwow puts copper plugs at roughly 20,000 to 30,000 miles, with platinum and iridium plugs running 60,000 to 100,000 miles or more. The RAC groups them the same way: copper shortest, platinum medium, iridium longest.
- Copper. Cheapest to buy, softest electrode, shortest life. Common on older and simpler engines.
- Platinum. A harder electrode tip that resists wear far longer. The middle option on price and life.
- Iridium. Hardest and finest tip, longest life, dearest to buy. Standard fitment on most modern turbocharged petrol engines.
This matters when you compare two quotes. A £110 quote using copper plugs and a £190 quote using the iridium plugs your engine was designed for are not the same purchase, and the cheap one may be back in two years. Ask which type is being fitted, and if the manufacturer specifies iridium, fit iridium.
Your service schedule is the real authority for your car, so the handbook beats any figure on this page. If you bought the car second hand and have no idea when the plugs were last done, a full service history is the first place to look, and if the paperwork is silent a garage can simply remove one plug and read its condition. Where plugs sit in the wider schedule is covered in what is included in a full service, interim versus full service and how often you should service your car.
Signs your spark plugs are worn
Worn plugs produce a spark that is still there but no longer strong or consistent enough to light the mixture cleanly every time. Carwow and Protyre list much the same symptoms, and they are all things you feel from the driving seat rather than see under the bonnet:
- Misfire or hesitation. A stumble or jerk as you accelerate, worst under load such as pulling away uphill. If the car feels flat generally, why is my car losing power covers the other causes.
- Hard starting. Longer cranking than usual, especially on a cold damp morning. Worth separating from a battery fault, which why will my car not start and car battery warning signs both go into.
- Rough idle. The car shakes or feels uneven at a standstill rather than sitting smoothly.
- Poor fuel economy. Fuel that is not burnt properly is fuel wasted. Protyre says a new set can improve fuel efficiency by up to 30 per cent, though that figure describes a car with badly worn plugs rather than a typical one, so treat it as the ceiling and not the expectation.
- Engine management light. A modern car detects a misfire and logs it. A flashing light rather than a steady one means stop driving, because that is the warning that raw fuel is reaching the catalytic converter. See why is my engine management light on.
- Knocking or pinking. A metallic rattle under acceleration can come from the wrong heat range plug or a badly worn one. Our guide to engine knocking noises separates the harmless from the serious.
- Black smoke. Unburnt petrol leaving the exhaust. What exhaust smoke colour means explains how to read it.
None of these symptoms is unique to spark plugs, which is exactly the problem. Coils, injectors, the airflow sensor and a vacuum leak all produce a similar misfire, and this is where a proper diagnostic check earns its £40 to £80. Reading the fault code tells the garage which cylinder is missing, and that turns guesswork into a targeted repair.
Can worn spark plugs fail an MOT?
Not directly. There is no spark plug inspection anywhere in the MOT, and the tester will not remove one. You can fail because of them indirectly, on emissions.
Under section 8.2 of the DVSA MOT inspection manual, the basic emissions test for a petrol car looks for:
- CO up to 0.2 per cent at fast idle, between 2,500 and 3,000rpm
- HC up to 200ppm at fast idle
- Lambda between 0.97 and 1.03 at fast idle
- CO up to 0.3 per cent at idle, between 450 and 1,500rpm
Emissions above the manufacturer limits or the default limits, or a lambda reading outside that range, are recorded as a Major defect, which is a fail. HC is the measure of unburnt fuel, so a car misfiring on a dead plug is pushing exactly the reading the test is looking for.
The sensible sequencing is to sort a known misfire before test day rather than on it. A fault you already know about is a repair you can shop around for. The same fault found on the ramp is a fail, a retest and whatever the testing garage quotes while your car is in their bay. Our guides to how to prepare for your MOT, what is checked in an MOT test and why cars fail their MOT cover the rest.
The expensive reason not to wait
A misfire is not just a rough running engine. Every time a cylinder fails to fire, its charge of petrol goes out through the exhaust unburnt and lands in the catalytic converter, where it burns instead. That overheats the ceramic honeycomb inside and can melt it.
This is the whole argument for dealing with plugs promptly. A set of plugs fitted is around £150. A replacement catalytic converter is a different order of expense entirely, as our catalytic converter cost guide sets out, and it is a bill created by driving on rather than by the original fault. A flashing engine management light is the car telling you this is happening now.
What else the garage may want to change
The usual suggestion alongside plugs is ignition coils, and it deserves a straight answer rather than a reflex yes or no. Coils and plugs are separate parts on separate lifespans. A coil is normally replaced because it has failed, not on a schedule, so the question to ask is whether this coil has actually been tested or is being replaced on suspicion.
Fair reasons to do coils at the same time: a fault code has named a specific cylinder and the coil has been swapped to another cylinder and the misfire followed it, or the car is high mileage and the coils are original and already off the engine anyway. Weaker reasons: a general recommendation with no test behind it, or all four coils sold on the strength of one bad one.
Ask for the labour to be quoted separately for each part, so you can see what you are really paying for the addition rather than accepting a single lump. If a quote feels padded, signs a garage is overcharging you is a short read that pays for itself, and there is nothing wrong with taking the car elsewhere for a second opinion.
How to keep the cost sensible
Bundle it with a service
This is the biggest saving available on this job. If the plugs are due and a service is due, having both done in one visit means you pay the strip down labour once instead of twice. On an engine where the manifold has to come off, that can be an hour or more of labour you simply do not pay for. Our car service cost guide gives the going rates, how long a car service takes covers the time, and oil change costs is the other item worth combining.
Get the quote split into parts and labour
A proper quote names the plug type and part number, gives the price per plug, states the labour hours and the hourly rate separately, and says whether any gaskets are needed if the manifold comes off. A single total tells you nothing and cannot be compared with the garage down the road. Two or three written quotes against the same registration cost you nothing and regularly save £50 or more on this job.
Use an independent garage
Independent garages are typically well below main dealer hourly rates for identical work, which main dealer versus independent garage sets out in full. If the car is still under warranty, servicing at an independent does not void it as long as the schedule and the correct parts are used, and does servicing at an independent affect your warranty explains the rules. A mobile mechanic can be a good fit where the plugs are easy to reach, and a poor one where the engine needs stripping on a driveway.
Booking a spark plug change
This is a job where the quote depends on your exact engine, so it genuinely pays to ask more than one garage. Put your postcode in and compare local garages, check their ratings and opening hours and send a booking request in about a minute. Give them your registration, say whether the car is misfiring or simply due on mileage, and ask which plug type they will fit and how many hours they have allowed. You pay the garage directly, and there is no booking fee.
If you want to sanity check the replies first, how to choose a good garage is a short read, and car service costs in Birmingham gives you a feel for local labour rates before you pick up the phone.
Key takeaways
- A full set fitted usually costs £100 to £250. The RAC gives an average of around £153 and manufacturer examples from about £121 on a Toyota to about £186 on an Audi.
- The parts are the small half of the bill. Plugs are often £4 to £25 each, so labour at £60 to £100 an hour is what moves the price between garages.
- Diesel cars do not have spark plugs. They have glow plugs, which do a different job and are only used to help the engine start from cold.
- Intervals vary hugely by plug type. Copper plugs want changing around every 20,000 to 30,000 miles, while platinum and iridium plugs can run 60,000 to 100,000 miles or more.
- Worn plugs rarely announce themselves as worn plugs. They show up as a misfire, a hesitation, hard starting, poor fuel economy or an engine management light.
- There is no direct spark plug check at the MOT, but plugs bad enough to upset combustion can push the car past the emissions limits in section 8.2, which is a Major defect and a fail.
- A misfire left running can destroy a catalytic converter, which turns a job worth about £150 into one worth many hundreds. That is the real cost of waiting.
- Ask the garage to split parts and labour on the quote, and to name the plug type. A set of iridium plugs and a set of copper plugs are not the same purchase.
Frequently asked questions
How much does it cost to change spark plugs in the UK?
Most drivers pay £100 to £250 for a full set fitted on a normal four cylinder petrol car. The RAC gives an average of around £153, with manufacturer examples running from about £121 on a Toyota and £126 on a Ford up to £177 on a BMW and £186 on an Audi. Treat those as markers rather than a price list. The spread within one badge is wider than the gap between two badges, because it is driven by how hard the plugs are to reach on your particular engine.
Do diesel cars have spark plugs?
No. A diesel engine ignites its fuel by compression, so it has no spark plugs at all. What it has instead are glow plugs, which warm the combustion chamber to help the engine start from cold and then stop doing anything once it is warm. They are a different part with a different failure pattern and a different price. If you drive a diesel and a garage has quoted you for spark plugs, ask them to clarify what they actually mean before you agree to the work.
How often should spark plugs be replaced?
It depends entirely on the type of plug fitted. The RAC puts the full range at every 20,000 to 150,000 miles depending on quality. Copper plugs are the shortest lived at roughly 20,000 to 30,000 miles, while platinum and iridium plugs commonly run 60,000 to 100,000 miles or more. Your service schedule is the authority for your car, so check the handbook rather than a general rule. If you do not have the history, a garage can pull one plug and read its condition.
What happens if you do not change your spark plugs?
The engine runs progressively worse before anything breaks. You get a weaker spark, incomplete combustion, a misfire under load, worse fuel economy and eventually an engine management light. The expensive part is what a long running misfire does downstream: unburnt fuel passes into the exhaust and cooks the catalytic converter, so a job worth about £150 can turn into a catalytic converter bill of many hundreds. A misfire is worth acting on within days, not months.
Can worn spark plugs fail an MOT?
Not directly. There is no spark plug inspection in the MOT, and the tester never removes one. Plugs bad enough to upset combustion can fail you indirectly on emissions. Under section 8.2 of the DVSA MOT inspection manual, the basic test wants CO up to 0.2 per cent and HC up to 200ppm at fast idle, with lambda between 0.97 and 1.03. Exceeding the limits is a Major defect, which is a fail. A car with a live misfire is a poor bet on test day.
How long does a spark plug change take?
On a straightforward four cylinder engine where the plugs sit under coil packs at the top, about an hour is normal. Some engines make it much harder. Where the inlet manifold has to come off to reach the rear bank of a V6, or where the plugs sit deep in wells that have filled with oil or grit, the job can run to two or three hours. That is why it is worth asking for the labour time on the quote rather than just the total.
Should I change the ignition coils at the same time?
Not automatically. Coils and plugs are separate parts with separate lifespans, and a coil is usually replaced because it has actually failed, not on a schedule. If a garage recommends coils with the plugs, ask which cylinder the fault code pointed at and whether the coil has been tested or just assumed. It is a fair recommendation on a high mileage car with a proven coil fault, and an expensive add on if it is being sold on a hunch.
Is changing spark plugs a DIY job?
On some cars it genuinely is, and on others it is a good way to create a much bigger bill. The risks are real: plugs thread into an aluminium cylinder head that strips easily, they need a torque wrench rather than a firm arm, the ceramic insulator cracks if it is knocked, and many modern plugs come pre-gapped and must not be adjusted. If the plugs are on top of the engine, you own a torque wrench and you have the correct part number, it is approachable. If the manifold has to come off, pay someone.