Why does the safety relief valve open each time the burner operates on a hot water boiler?

The safety relief valve in a hot water boiler is designed to open under certain conditions to prevent overpressure or overheating, which can be dangerous. When the burner operates, it heats the water, causing it to expand and create pressure within the system. If the expansion tank is waterlogged, it means that the air cushion, which is responsible for absorbing the thermal expansion of the water, cannot accommodate the additional volume created by the heated water. As a result, the pressure in the boiler system can rise excessively because there's no room for the expanded water to go.

In this scenario, the safety relief valve will open to release the pressure and prevent potential damage or failure of the boiler system. It's critical to maintain a functioning expansion tank so that it can properly handle the changes in volume due to temperature fluctuations.

In contrast, temperatures that are too high could theoretically cause the valve to open, but they are typically managed by the temperature controls and safety mechanisms of the boiler itself. Similarly, while adjustments to the burner could potentially affect efficiency and performance, they do not directly relate to the immediate functioning of the safety relief valve as it pertains to pressure management due to thermal expansion.