Your boiler uses electrodes in order to ignite and heat up your home. However, over time, these components can become dirty and this may prevent your boiler from working.

There maybe two types of electrodes present in your gas boiler: ignition electrodes and flame-sensing electrodes (sometimes also known as an ionisation probe). The ignition electrode, as you can probably guess from its name, is responsible for creating a spark that will ignite the gas supplied by your boiler. The ionisation probe acts as a safety device. It is able to sense when there is a flame present in the burner. If it cannot sense a flame, it will turn the gas off to prevent the boiler from supplying gas that isn’t being burnt.

The ignition electrodes and ionisation probe are usually positioned together in the combustion chamber of a boiler. Ignition electrodes can be used as ionisation probes and vice versa.

Either of these sensors can become dirty over time, which could prevent them from working. If your boiler isn’t starting up, or does start up and quickly turns off, your electrodes may need cleaning. The electrodes and burners are usually checked during your boiler’s annual service. If they need a clean, the Gas Safe registered engineer should be able to do this for you during the service. 

What are electrodes made of?

The materials that are used for electrodes must have certain properties to ensure that they work effectively. These properties include good conductivity, resistance to corrosion and hardness. Copper, graphite/carbon, titanium, brass, silver and platinum can all be used for electrodes, however each of these materials will be better in relation to certain features than others. For example, copper has a high electrical conductivity but its oxidation resistance isn’t as good as that of silver.

Copper is a popular material for electrodes. Its high conductivity and strength make it ideal, however it can be quite expensive. For this reason, some electrodes will be made from other metals. Titanium has excellent resistance to corrosion, however it isn’t as easily accessible. Brass is expensive, has a lower conductivity and isn’t as hard-wearing, but in some applications this can be beneficial. It is quite easy to machine and can be moulded into nearly any form. Silver has the highest conductivity, however it’s quite a soft metal, which might make it unsuitable for some applications.

Each metal has its own advantages and disadvantages and will likely be picked depending on what it’s being used for and cost. 

Why are electrodes made of graphite?

Graphite is one of the most popular materials for electrodes. Its high electrical conductivity and its capability to withstand high temperatures make it ideal for use in boilers.

Its unique structure is what makes it so perfect in electrodes. Each carbon atom within the graphite is joined to three other carbon atoms via covalent bonds. For every carbon atom, there’s one non-bonded electron that is able to roam freely. The way in which the atoms are built up creates layers that the delocalised electrons can move between. It is this movement that makes graphite such a good conductor of electricity.

Graphite has a high melting point, which allows it to conduct electricity even in really high temperatures. This material is more readily available than many other substances, and can even be created synthetically. This makes it more cost-effective than materials such as brass, silver and copper. 

How to clean electrodes

If you’re worried that your boiler isn’t functioning because of grubby electrodes, having them cleaned is a relatively easy and cheap task.

To clean your boiler’s electrodes, it is necessary to remove the front casing to access some specific parts. It is the law that only a Gas Safe registered engineer can do this, so you shouldn’t attempt to clean the electrodes yourself.

The engineer will likely shut off the power to the boiler and remove the front casing. They will locate and remove the electrodes and probably use a small piece of light grit sandpaper or an emery cloth to remove the excess carbon from the sensors. It’s a relatively quick job that can be completed during the boiler’s annual service to ensure that it’s running safely and effectively.

The engineer will re-fit the sensor and turn the boiler back on to make sure that it’s working. If the sensors are broken rather than simply dirty, they will need replacing. 

Do graphite electrodes need to be replaced regularly?

When both anode and cathode electrodes are made from graphite, they become oxidised over time. As oxide ions lose electrons, excess oxygen is created. This additional oxygen reacts with the carbon in the electrodes and they gradually burn away. This can happen over a long period of time, so your graphite electrodes shouldn’t need replacing that frequently. However, it’s possible that your electrodes might not be dirty, but instead worn down. 

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