Yes i know its a Wilesco product but it is suitable for Mamods as well !  Also other small model boilers .   After a long time in research and development Wilesco is able to present a decalcifying agent for steam boilers. One unit contains a 100 ml bottle of decalcifier and  detailed instructions on how to use it. The boiler should be filled with a mixture of this liquid and water. After leaving for 24 hours to soak empty the boiler and the engine can be restarted immediately.1 item is 1 bottle. 50mm of descaler should do it for most Mamods.