Why and when to replace the electrodes on a Worcester Bosch boiler. Spark electrodes on modern boilers replace the need for a pilot light meaning that when there’s a demand for heat the boiler can fire up instantly, so it goes without saying electrodes get a lot of use and wear and tear will occur. In fact most boiler manufactures dont cover electrodes under warranty because they should be replaced when carrying out the annual service, anywhere between every 3 to five years depending on ...