charging tenants for a repair

[Max T.]

So I have a student rental (Temple University) with 3 young men living in a 4 bedroom/2 bathroom house. I've been managing this rental with them for the past year and a half. They are good nice kids, but they don't know too much about taking care of a home. 

I've had a lot of service calls about the washer and dryer. The first was a broken drive coupling (washer) shortly after I acquired the building. The second was a bad heating element in the dryer. Both repairs I paid for as normal wear and tear.

The third service call was for the dryer again. Nothing was wrong with it. It had not been drying properly because the tenants were not cleaning out the lint trap. My repair man did not charge me for his trip out of appreciation for some recent referrals I had given him (lucky me!). At that time I did let the tenants know that this service call was not due to normal wear and tear, but to tenant misuse, and that had I been charged I would have billed them for it.

Today I get a call from my repair man. The tenants had scheduled a washing machine repair without telling me. I addressed that with them. Furthermore, the washer needed its drive coupling replaced again! This is the second time in less than a year and a half, and my repair man tells me it is due to washing over-sized loads. He also told me that in conversation with the tenants during the repair work they mentioned that they try to get a lot done at once.

I asked my repair man to include that analysis on his invoice, and also note that this is the 2nd time this part has been replaced in the past 2 yrs.

I just let the tenants know that I will be billing them for the cost of this repair............... Am I justified?