Maintenance - Electrics

Maintenance

21 Sept My Tenants phoned me (Sunday evening) stating problems with the electrics. The same night they decided to move out to their dad's house and lived there until they found a 'new' rental property.
22 Sept (Monday) I got an electrician in to repair the electrics.
23 Sept The electrician said the house isn't safe to live in.
25 Sept I repaid the tenants their rent from 22 Sept for 16 days as their tenancy agreement with me is suppose to end on 7 Oct 2014.
28 Sept 2014 the tenants returned my house keys, after removing all their items.
The tenants have now threatened to sue me can they? (I didn't know the electrics were dangerous. I had a consumer box fitted almost 10 years ago and is/was due for an inspection next January 2015. Also, the tenants washing machine pipe was dripping water on my washing machine plug socket.)