for anyone with slow heating calorifier (Quick B3 – 20l) – I recently got a B37 cruiser which had spent its life on the south coast and I had a problem with the water taking ages to heat up – couldn’t find an obvious problem so changed it (and upgraded to a larger one) – anyway when I took it and removed the immersion it was caked in limescale. I brought some FERNOX DS-3 LimeScale Remover and filled the tank will it mixed 1:10 – totally amazing results and tested it at home with the immersion and heats fully in a fraction of the time. And now the boat is in Scotland with our lovely soft water hopefully won’t need to do it again 😀