What is that tank there?
The question relates to an expansion tank found on water boilers. When the water inside the boiler is heated the water expands. The space in the expansion tank provides room for the water to expand as it is heated. Inside the expansion tank there is water and air. As the boiler heats up it takes up some of the space provided by the air in the expansion tank. The expansion tank is normally located above the boiler. Some of these tanks are sometimes attached to the ceiling. More modern expansion tanks are connected right above the boiler. The main issue with old expansion tanks is that they can completely fill with water over time. When this occurs there is no room for the pressure to expand. As a result the boiler pressure relief valve may expel. To remedy this issue the older expansion tank should be emptied by a heating professional to avoid this issue. The more modern expansion tanks have a bladder or diaphragm that is installed inside the tank. The diaphragm prevents the water and the air from mixing and thus the issue of the tank filling with water is alleviated. For the most part modern expansion tanks are maintenance free. If the tank is leaking, damaged or rusted out the tank must be replaced by a heating professional.