I figured I should ask this as it's kind of a specific case. Basically my mom and dad moved into a place probably 15 years ago, and for years my dad did all the repairs/snow removal/landscaping/general maintenance etc., Usually free of charge or with the landlords paying for parts, because he liked doing DIY stuff and didn't mind.
However my parents have been divorced for two years now, and my mom still lives in the property where the landlords got so comfortable not paying for anything that she waited 11 months for her oven to be fixed and 6 months for her refrigerator until I finally just paid to fix it.
Now she got oil for her heat(she's been using electric ones for a while) and because the landlords have neglected yearly maintenance on the boiler the gaskets are in multiple pieces and it was completely full of 10+ pounds of God know what. I cleaned it but her landlord swears the rope gasket(in 4 pieces) and the regular cracked and crumbling gasket are both fine when it is clearly letting smoke out of the opening. At this point I'm ready to just pay a friend that does HVAC to replace the seals but I'm not doing it on mine or my mother's dime. To be clear, the last time the boiler was actually serviced with 2007, the first year they lived there, since then they have failed to schedule any yearly tune-up, cleaning, etc.
It's clear the landlords have neglected regular maintenance or repairs, so at what point am I allowed to simply fix it and deduct the cost from the rent(as landlordology says is an option)?