HW baseboard heating, smokey burner,and cleaning is this fair?

[Colleen F.]

SF unit with hot water baseboard. Tenant calls saying the oil burner off the kitchen started  smoking up kitchen/dining area. Turned off the furnace and accelerated the furnace cleaning by 1 week. Furnace was fine, maybe due to dregs of oil tank. I was there for the furnace cleaning and wiped down kitchen and dining area as the tenants left after the sooting for  month long family visit and I had to do something while the guy was doing the furnace. At that time  I did not see any soot beyond those areas. Turn the furnace back on, checked it twice while they were away,  It was fine.  They come back and two days later say it is leaking, water , it needs air vent replaced and control panel (leaked on)  but no sooting. Could be something they did, maybe ,maybe not. 

 I prorated rent for the days they had no heat and had to use electric (48 hours) and credited for cleaning. They said cleaning was more extensive (they say it went up to the second floor)so I made an additional credit , they also say they lost food which I ignored because I can't fathom how that could be due to this issue.  Anyway in the interim their rent check had bounced so I wasn't sending a cleaner.  

What would you have done?   And for the heating guys out there would you expect < 10 minutes  of sooting with HW baseboard to spread to the second floor?  Can an air vent (HW baseboard) be damaged by the tenant banging it? heating guy says "sometimes they just fail"  I am charging late and return check fees so I think they are just looking for more but I feel I have been fair.