Glow Plug Buying Guide
Last updated: 24 April 2026
Glow plugs heat the combustion chamber in diesel engines to aid cold starting. Failed glow plugs cause hard starting in cold weather, rough idle until the engine warms up, and white exhaust smoke. Seized plugs are a common complication during removal. At CarParts247 we stock glow plugs from Bosch, NGK, and Beru for all popular diesel engines.
Glow plug failure symptoms
Glow plug failure is most noticeable in cold weather. One failed plug may cause slight roughness; multiple failures can prevent the engine from starting entirely.
- Hard or extended cranking in cold weather — glow plugs not heating properly
- Glow plug warning light stays on or flashes — ECU detected a fault
- White smoke from the exhaust on cold start — incomplete combustion
- Rough idle for the first few minutes until the engine reaches temperature
- Misfire codes on specific cylinders during cold start
Removal tips for seized plugs
Glow plugs seize in the cylinder head due to carbon build-up and corrosion. Forcing a seized plug risks snapping it in the head — a costly repair.
- Warm the engine before attempting removal — thermal expansion helps free seized plugs
- Apply penetrating oil to the plug threads several days before attempting removal
- Use the correct deep socket — glow plugs are fragile and snap easily
- If the plug won't turn, stop immediately — specialist removal tools or reaming may be needed
- Consider replacing all glow plugs at once — they are the same age and condition
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Diesel cold-start problems — glow plug failure symptoms, removal tips for seized plugs, and replacement advice.
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Frequently Asked Questions
How long do glow plugs last?
Most glow plugs last 80,000-100,000 miles. Modern ceramic glow plugs (PSG16 type) can last longer. Replace them proactively before winter if they are high-mileage.
Can I drive with a faulty glow plug?
Yes, once the engine is warm it runs normally. However, cold starts will be difficult and the engine will run rough until it warms up. In very cold weather, the engine may not start at all.
Why do glow plugs seize?
Carbon deposits and corrosion bond the plug thread to the cylinder head. Short journeys that don't fully warm the engine, and infrequent removal, increase the risk. Preventive removal and anti-seize compound on new plugs help.
What happens if a glow plug snaps during removal?
The broken tip must be extracted from the cylinder head. This requires specialist tools and sometimes removal of the cylinder head. It is a costly repair, which is why gentle removal technique is essential.
How much does glow plug replacement cost?
The price of glow plugs depends on your exact vehicle and the brand you choose. Enter your registration above to see parts confirmed to fit, then compare prices from the brands we stock on this page. Free UK delivery on orders over £50.
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