I'm thinking of fitting a magnetic filter in our central heating system, having replaced a few microbore plastic pipes that were full of black crystalline "stuff". It's an old oil boiler (Worcester Heatslave). I gather these filters should be fitted in the return line from the radiators and I think I have found a reasonable place to put it, in a vertical run of pipe. Could anyone offer any recommendations as to which one? There seem to be quite a few out there! There are 14 radiators in the house, of which four are doubles, if that makes a difference?