What are the remedies available to the landlord for the breach of contract by the tenant?
Your question assumes that the tenant was negligent and that the repair needed was not the responsibility of the Landlord. If the tenant was not negligent as provided in your agreement then a question remains about whether as landlord, you would have been responsible for the repairs under the Connecticut Landlord Tenant Laws. See Section 47a-7 below.
Sec. 47a-7. Landlord’s responsibilities.
(a) A landlord shall:
(1) Comply with the requirements of chapter 368o and all applicable building and housing codes materially affecting health and safety of both the state or any political subdivision thereof;
(2) make all repairs and do whatever is necessary to put and keep the premises in a fit and habitable condition, except where the premises are intentionally rendered unfit or uninhabitable by the tenant, a member of his family or other person on the premises with his consent, in which case such duty shall be the responsibility of the tenant;
(3) keep all common areas of the premises in a clean and safe condition;
(4) maintain in good and safe working order and condition all electrical, plumbing, sanitary, heating, ventilating and other facilities and appliances and elevators, supplied or required to be supplied by him;
(5) provide and maintain appropriate receptacles for the removal of ashes, garbage, rubbish and other waste incidental to the occupancy of the dwelling unit and arrange for their removal; and (6) supply running water and reasonable amounts of hot water at all times and reasonable heat except if the building which includes the dwelling unit is not required by law to be equipped for that purpose or if the dwelling unit is so constructed that heat or hot water is generated by an installation within the exclusive control of the tenant or supplied by a direct public utility connection.
(b) If any provision of any municipal ordinance, building code or fire code requires a greater duty of the landlord than is imposed under subsection (a) of this section, then such provision of such ordinance or code shall take precedence over the provision requiring such lesser duty in said subsection.
(c) The landlord and tenant of a single-family residence may agree in writing that the tenant perform the landlord’s duties specified in subdivisions (5) and (6) of subsection (a) and also specified repairs, maintenance tasks, alterations, or remodeling, provided the transaction is entered into in good faith and not for the purpose of evading the obligations of the landlord.
(d) The landlord and tenant of a dwelling unit other than a single-family residence may agree that the tenant is to perform specified repairs, maintenance tasks, alterations or remodeling if (1) the agreement of the parties is entered into in good faith; (2) the agreement is in writing; (3) the work is not necessary to cure noncompliance with subdivisions (1) and (2) of subsection (a) of this section; and (4) the agreement does not diminish or affect the obligation of the landlord to other tenants in the premises.
Assuming that the repair was not your responsibility, then you can terminate if the Tenant violated the lease.
Chapter 830, of the Connecticut General Statute §47a-11c, discusses the Rights and Responsibilities of landlord and tenant in case of breach of the rental agreement by the tenant and measure of damages.
“If a landlord terminates a residential or commercial tenancy on the grounds that the tenant committed a breach of the rental agreement and the landlord brings an action for damages for the breach, such damages shall include the amount of rent agreed to by the parties but unpaid by the tenant. The landlord shall be obligated to mitigate damages. This section shall not limit either party's rights to assert other legal or equitable claims, counterclaims, defenses or set-offs.”
Therefore, you can sue your tenant and terminate the contract for the breach. You can claim the rent from your tenant that is not yet paid by him.