You will need unoccupied property insurance - try a company called Ocaso - they will insure the property whilst unoccupied and then change the policy to a let property once sorted.
Only a few companies do this, mostly you have to take out specialist unoccupied policies, cancel and then get a property owners.
They will ask that certain precautions are taken whilst unoccupied - such as the water being turned off (prevents pipes bursting!), or the heating being left on etc. You shall also need to inform them of the water pipe bursting as it is a material fact, and the property will technically not be well maintained (another general stipulation) - you will most probably only get FLEA cover whilst your property is unoccupied and under renovation due to the additional risks - FLEA is Fire Lightning Explosion/Earthquake and Aircraft - only claims resulting from these causes will be covered.