Help! I have a Baxi back boiler that has been functioning very well and was last serviced in January 2014. Today, the hot water has turned very discoloured (almost black) but remains very hot. I have tried the central heating to ensure the system is working ok, and all is well. I have tried to run the hot water through to clear the dirty water, but the water remains coloured (not as much as before). Does anybody have any further ideas?