Of course a steam engine needs… steam. (Brilliant.) On Shieldhall, that’s provided by two ‘Scotch Boilers’ – and they take quite a bit of cleaning. (See picture with me on camera staying well clear of the action.) For why? Well the boiler is basically a big kettle, but big enough to make a gazillion cuppas. Under the big round boiler is an L- shaped furnace. The heat from the fire lit beneath shoots up the upright bit of the L, and into dozens of tubes inside the boiler – which is surrounded by a jacket full of water. Which becomes steam. The remaining heat etc from the tubes goes out up the funnel. But burning fuel means soot – and if you accumulate too much, just like a furred-up kettle, the boilers don’t work very well. Hence the big clean. Mucky, but essential.