The first thing is to raise the matter with the supplier - If you have followed the advice in question 1, you'll be checking the job before signing or paying for it. This is the best stage to get any problems rectified - while the fitter or installer is still on site and is waiting for you to approve the work. Don't sign any job sheet or make full payment untill you are happy with the work.

If it is not possible to resolve the matter straight away or the problem develops later on, you should phone the supplier immediately. Explain exactly what the problem is and ask how and when the supplier intends to rectify it. Keep a record of any phone calls and make notes of who you have spoken to and what was said - also keep copies of all contracts, invoices, job sheets, letters etc. If you are not happy with the response you get, ask to speak to the manager or owner of the company - With a reputable company the vast majority of problems are resolved at this stage or earlier.

If you are still unsatisfied, write to the company using recorded delivery. Address the letter to the manager or owner and state what the problem is and what you want done to remedy it. Don't get angry or abusive - just lay out the facts and say you are allowing a reasonable period of time (usually 14 days) for the supplier to respond and rectify the problem.

For more information contact the citizens advice bureau.