Not the easiest problem to rectify without technical know how. It would appear that the multi point lock has given up the ghost and needs replacing, a simple enough job with the doors open providing you can identify the exact model of M.P.L. but opening the doors without causing a considerable ammount of damage to the doors is not easy unless you are trained properly. I would strongly advise you to call in your local locksmith, he will gain access quite quickly without damage and be able to identify the M.P.L and order a new one for you. I am a trained Locksmith and I have attended clients who have tried the D.I.Y. entry approach and ended up paying hundreds of pounds to rectify the damage they have caused. Please heed this advice and leave this one to an expert.
Brian, February 2011
