Built in 1893, the Derby Castle Boiler House originally housed two 120psi Galloway Boilers (a third was installed in 1894), used for powering the Manx Electric Railway and its equipment. Water for the boilers was supplied by two nearby streams which fed into a underground storage tank. A 60ft chimney was also installed alongside.
The building were demolished in 1904, following the decision to draw from AC power at the Laxey Power Station instead. The rotary and switchboard were then moved inside the Engine House, which later became the Machine Shop.