Negotiating Fair Compensation for Repair Delays

I informed the tenant I was going on holiday; his boiler broke down while I was away, so there was a delay in picking up his message. My usual plumber was unavailable, so I arranged for someone to visit, and the boiler was repaired -it was only low pressure. From the initial text, to repair was nine days. The tenant is now asking for compensation at 25% of a month's rent. Is this correct?

View Related Handbook Page

Landlords’ Responsibilities for Repair and Maintenance

In addition to any repair responsibilities explicitly set out in the tenancy agreement, common law and statute will imply terms to the agreement between landlord and tenant.