I started a thread this past winter where I wasn't getting my oil furnace temp over 130 , well the main problem was my y-strainer was clogged with what looked like a bunch of crushed egg shells . Now this was my first year with all new furnace pipe etc. .I've talked with my furnace co. and some other guys that make a living in the heating buss. and everyone is telling me its a lime calcium mineral deposit . I just finished up flushing the system out about a weeks worth in the evenings trying to get all of this stuff out of the system , it just keeps coming , well I finally think I have most of it out . A guy I know that manufactures heat exchangers and is very up on hot water systems says I'm going to have this problem every year unless I use either distilled water or water that hasn't been in the ground collecting minerals , such as rain water .What I don't get is I haven't heard anyone I know with a OWB having the same problem , anyone here heard of anything like this ???????