If you fixed within 10 days that is reasonable.
Any claim can only be under S.11 of the Landlord and Tenant Act 1985 which says:
11 Repairing obligations in short leases.
(1)In a lease to which this section applies (as to which, see sections 13 and 14) there is implied a covenant by the lessor—
(a)to keep in repair the structure and exterior of the dwelling-house (including drains, gutters and external pipes),
(b)to keep in repair and proper working order the installations in the dwelling-house for the supply of water, gas and electricity and for sanitation (including basins, sinks, baths and sanitary conveniences, but not other fixtures, fittings and appliances for making use of the supply of water, gas or electricity), and
(c)to keep in repair and proper working order the installations in the dwelling-house for space heating and heating water.
[F1(1A)If a lease to which this section applies is a lease of a dwelling-house which forms part only of a building, then, subject to subsection (1B), the covenant implied by subsection (1) shall have effect as if—
(a)the reference in paragraph (a) of that subsection to the dwelling-house included a reference to any part of the building in which the lessor has an estate or interest; and
(b)any reference in paragraphs (b) and (c) of that subsection to an installation in the dwelling-house included a reference to an installation which, directly or indirectly, serves the dwelling-house and which either—
(i)forms part of any part of a building in which the lessor has an estate or interest; or
(ii)is owned by the lessor or under his control.
Given it was repaired within 10 days this is a reasonable period. Especially given yo had provided 2 portable heaters.
You can defend the claim - it will fail against you
Can I clarify anything for you about this today, please?
If you need anything further I am available for a follow up at no extra cost.