It sounds like you have a good "case". Certainly, on its face, it appears that the Landlord is not honoring your agreement, and it looks like you'll need an attorney to get involved to get this solved. HOWEVER, may I suggest the following. The person who gave you the bid must also have a sense of "why" this occurred. Both you and your landlord will each spend money on attorneys battling this out, and, at $500, it is fair to say that at a minimum, together you will spend $500 on attorneys and the pump will still need to be fixed! So, ask the person what they think. If the Landlord doesn't like the answer, ask the Landlord to send his/her own person for an opinion. If there's then a conflict, perhaps a third and deciding party? My point is that while you may have a slam dunk case, you may end up spending more just to prove you're right if you have lawyers involved.
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