how can i fix door latch?

its nothing to do with barrel its you lock strip thats the prob,you will need to take full lockstrip out and see if you can oil it to free the catch,if not replace with a new 1,there should be a make stamped on the strip so you get the right 1.its not the easiest job if your not confident in this type of thing but if you are doing it yourself you have to take handles and barrel off first before the lockstrip will come out.hope this helps

shaun www.sdwupvcrepair.co.uk
March 2008