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

The safety relief valve opens when the expansion tank is water logged because a waterlogged expansion tank cannot properly accommodate the pressure changes that occur as the water in the boiler heats up. As the water temperature rises, it expands, increasing the pressure within the system. The expansion tank serves the purpose of absorbing this pressure increase by providing some additional space for expanded water. When the tank is water logged, it is filled with water and cannot expand further, leading to excessive pressure build-up. As a safety mechanism, the relief valve will open to release this pressure, ensuring the system remains safe and preventing potential damage or failure.

In the context of the other options, a boiler being underfilled would typically result in insufficient water volume to operate effectively, but it would not necessarily cause the relief valve to open. Furthermore, if the burner were malfunctioning, it could lead to various operational issues, but it wouldn’t directly correlate to the relief valve opening consistently. Lastly, if the pressure were too low, the relief valve would not need to open since it is designed to release excess pressure, not to respond to low-pressure conditions. Thus, the condition of a waterlogged expansion tank is the key aspect affecting the operation of the safety relief valve in this scenario.