What happens to boiler water level when boiler is fired will it fall or rise?

Water does not expand with heat the way hydrocarbons do. Thus, from an expansion perspective, the water level will not change as the temperature increases. *To correct the answer listed above without deleting it, as I'm new here :) : Water is one of the few elements that expands in its liquid and solid states. The overall expansion is approximately 4%. There are two basic types of boilers used for hydronic heating, water and steam. The level of water in a steam boiler will drop when fired; as the liquid water becomes a gas, less liquid remains in the boiler. Any water boiler used for heating will be constantly "full" as it is essentially a sealed system. Due to the expansion of the water when heated, all liquid water heating systems use expansion tanks to account for this change in volume. correcting the answers listed above without deleting them Initially when a boiler is fired the water is heated and the steam starts to generate. During this time large amount of ebolution is taking place as the steam is trying to rise up through the water. This causes a swell in the water level and we actually sea a rise in the water level. when fired always waterlevel surges,it is seen practically