I was giving my boiler a wipe and rinse today as I always do, then I found that what I thought was discolouring of the plastic was actually gunk! I have managed to scrub loads off but is there somthing that will do the job with out all this elbow grease? Was thinking about boiling water with vinegar in it? Then of course a good proper rinse afterwards.... Or any other suggestions for something that I will have in stock in the house?