A boiler that includes a housing is disclosed. The housing houses a combustion chamber, a heat exchanger system, a heat flow path, an isolating member, and a removable panel. The heat flow path thermally couples the combustion chamber and the heat exchanger system. The isolating member at least partially separates the combustion chamber from the heat exchanger system wherein. When the removable panel is removed a user is provided access to the heat exchanger system. The isolating member is internal to the housing. The removable panel is an internal removable panel positioned on the isolating member. When the internal removable panel is removed, the user is provided internal access to the heat exchanger system. In other embodiments, the panel is an external removable panel positioned on an exterior wall of the housing. When the exterior removable panel is removed, the user is provided exterior access to the heat exchanger system.