Hello, can anyone help in the last week i treated my CH with kilrock cleanser and limescale remover (i could hear the scale in the pipes moving when the boiler fired up) but now my boiler comes on for only a few minutes making loud noises before shutting itself off, i have checked the pump and seems to be free ( i unscrewed the large screw on front of pump and the shaft turned freely) could it blocked somewhere ??? what should i try next ??