Before you instruct a supplier you should check the following:
That your landlord doesn't have a current contract that covers the issue in question eg. British Gas, Swale or Homeserve contract
That the issue isn't covered by the management company of the building (if relevant)
Ensure that the contractor you instruct has relevant industry qualifiations and insurances
If this is an issue you have already reported, check the work has not already been commissioned by your landlord/Sandersons. If you instruct the same work again you may not be reimbursed