My old probe for my MW-102 died. Bought a new SE220. Tried testing it out this morning but it reads nothing but 7.03 no matter what I test. If I put it in 4.01 solution, it reads Ec, telling me the solution is not correct. If I put it in my tap water, it reads 7.03 as well. Is there anything I can try to correct this or don't bother and return it?