Boiler Electrodes: Ignition, Flame Sensing & Maintenance Explained
In modern gas boilers, electrodes are small components with big responsibilities. Often hidden inside the combustion chamber, electrodes are crucial for igniting the boiler and monitoring the flame once it’s lit. Whether you’re a Gas Safe engineer, a landlord keeping properties in top condition, or a savvy homeowner, understanding the function, failure signs, and replacement tips for electrodes can save time, money, and reduce call-outs.
What Are Boiler Electrodes?
Boiler electrodes come in two main types:
- Ignition Electrodes: These create the spark that lights the gas when the boiler fires up.
- Flame Sensing Electrodes (or Flame Rectification Electrodes): These detect whether a flame has been successfully established and keep the boiler running.
Both types are usually made from metal rods enclosed in ceramic insulation and mounted near the burner. If either fails, the boiler will not ignite or will shut down shortly after ignition.
Why Electrodes Matter in Your Boiler System
A functioning electrode setup ensures:
- Safe and reliable ignition every time the boiler is called to heat water or radiators
- Confirmation that the flame is present, which allows the gas valve to remain open
- Prevention of gas buildup if no flame is detected
- Compliance with gas safety standards
Faulty or poorly positioned electrodes can mimic more serious issues, such as PCB faults, gas valve problems, or even fan failure, making accurate diagnosis key.
Signs of Electrode Problems
Boiler electrode issues typically show up as:
- Boiler fails to ignite or attempts multiple starts
- Boiler lights briefly, then shuts down with a fault code
- Popping or clicking noises during ignition
- Flame extinguishing quickly after ignition
- Repeated ignition lockouts
Error codes vary by brand but often reference ignition failure, flame detection, or gas valve issues. Always consult your boiler’s fault code manual to confirm.
Common Causes of Electrode Failure
- Carbon or soot build-up from incomplete combustion
- Cracked ceramic insulation from heat stress or age
- Worn or oxidised tips reducing spark strength
- Incorrect electrode gap due to movement or installation errors
- Electrical connection faults or PCB relay issues
Regular servicing should include inspecting and cleaning the electrodes, as even minor build-up can affect performance.
Key Benefits of Quality Electrodes
- ✅ Reliable boiler ignition – avoids cold starts and repeat resets
- ✅ Accurate flame sensing – ensures safety and compliance
- ✅ Compatible with leading boiler brands – including Worcester, Vaillant, Baxi, Ideal
- ✅ BSI-compliant refurbished and OEM parts available
- ✅ 12-month warranty on refurbished electrodes
- ✅ Tested to ensure correct resistance and spark strength
At NBS, all refurbished electrodes are thoroughly cleaned, tested, and inspected to ensure safety and performance.
Expert Insight
“Electrodes are often blamed too late. We always check them early when a boiler fails to light—it’s a common cause and an easy fix.” — Senior Gas Engineer, Leeds
“If the ceramic is cracked or there’s heavy oxidation, replacement is the only option. Ignition issues are often resolved just by sorting the electrode.” — Technical Advisor, NBS
When to Replace vs When to Clean
Replace If:
- Electrode tip is pitted, corroded, or heavily oxidised
- Ceramic insulation is cracked or damaged
- Spark is weak or fails to jump the gap
- Flame rectification signal is inconsistent or missing
Clean If:
- Minor carbon or soot build-up
- Electrode tip is intact with no visible damage
- Spark gap and mounting are correct
Use a soft wire brush or abrasive pad to clean the electrode gently. Avoid bending the electrode or damaging the ceramic sheath.
Installation & Testing Tips
- 🔧 Check manufacturer gap specs – incorrect spacing will prevent ignition
- 🔍 Use a multimeter to check resistance if applicable
- 🔥 Observe spark during ignition – it should be strong, blue-white and direct
- ⚠️ Never re-use a cracked electrode – even if it appears functional
- 🧰 Always isolate power and gas before electrode servicing or replacement
Electrodes are often replaced in pairs (ignition and flame sensor) for optimal performance. Find the correct ones for your boiler.
FAQs
How long do boiler electrodes last? Typically 3–7 years depending on usage and combustion quality.
Are refurbished electrodes safe? Yes, provided they’re tested and sold by trusted sources like NBS. All our refurbished parts meet BSI standards.
What’s the difference between spark and flame sensing electrodes? The spark electrode ignites the gas. The flame sensor confirms the flame is present and tells the boiler to keep running.
Can I clean the electrodes myself? If you’re experienced with boiler internals and have isolated the unit, yes. For most users, a Gas Safe engineer should handle it.
Can electrodes be adjusted? Only slightly, and only if recommended by the manufacturer. Poor positioning can lead to misfires or dangerous conditions.