Can anyone help? Two weeks ago I had to have the flue from my boiler changed due to a conservatory being built on the side of the house. It was changed from a horizontal flue through an external wall into a vertical one through the ceiling (it is a RS type). As soon as this was done my boiler started to lockout and would not work. We could reset it and it would work for a few hours before going out again. My plumber came back and fitted an extension to raise the flue to cure the problem but this has now made it worse and it will lockout after about 20mins now. My Plumber doesn't have a clue and has spent all day trying to fix it. The boiler worked fine before the flue was moved. Does anyone have any ideas so I can point the plumber in the right direction??