My fill valve is not filling. I adjusted the screw on top and I do not see pressure building in the boiler tank. Last fall I had a similar issue. Then I adjusted the screw a 1/2 turn and it adjusted pressure correctly. This year the screw seems to do nothing. I lowered it and raised it wil no affect. Boiled still only has 2psi. Does this unit fail in this way? There also seems to be a cleanout on the bottom. Is this another option to free the blockage? Or just replace?