Tenant’s right for terminating contract early

Do I have absolute legal right to reject my tenant request on early termination of contract after a gas leakage which was fixed within a day after this was raised? The flat has no gas cooking hob and has no other gas consuming facilities so no gas certificate was needed. The flat has been fitted with Carbon Monoxide detector and did the job for alarming the tenant. The tenant claimed she admitted to the hospital and had Carbon Monoxide detected within her blood but I am unsure I am actaully responsible for this as myself as a landlord I have fullfilled what I need before renting the property out and have the issue rectified immediately. There are pipes going through the flat thou and the central heating is done by gas but this is being managed and maintained by the block managing company and they have fixed the issue within a day so there isn't anything I could do quicker or better.