Tenants turned off heat, pipes froze. Advice needed

[Ian K.]

My tenants turned down the heat since they had purchased a home but were still under lease for a few weeks with my rental.  They turned the heat all the way down, I guess around 40 or 45 (it's past the last number of 50).  We got deep freeze and pipes burst.  I got it all repaired for about $1500 and a lot of my time.  The part of the lease that pertains to this states: 

"The Tenant(s) agrees to keep premises in good, clean condition, - to make NO alterations, including painting; to replace glass broken or cracked as a result of Tenant’s neglect or careless use of the premises, to repay the Landlord the cost of repairs made necessary by the neglect or careless use of the premises by theTenant(s), and to surrender the premises at the termination hereof in like condition as when taken, reasonable wear by the elements and ordinary wear and tear excepted."

There is nothing in the lease that says they have to keep the heat at a certain temperature. 

The deposit I have is $1575.  They were good tenants and left the place in otherwise good/fair condition.  

How would you handle this?  What would you charge the tenants? Thanks in advance