Please help - neighbour dispute!?

I live in a 4-plex and unfortunately had a falling out with the owners of the basement. She is now claiming that the outflow pipe from my boiler is dripping onto her outside space. The pipe in question comes from a condensing boiler which the freeholders installed (we are all leaseholders of the flats). I have not seen the pipe dripping ever - she is claiming that it drips intermittantly for half an hour every morning but I have no evidence of this. I have called 2 plumbers around but theycan not find anything wrong and have written a report to that effect. I have suggested getting a builder to install a drainage pipi from the outlet to the outside drain. The managing agent was initially in agreement with the plan but has recently emailed me to say that that solution is no longer acceptable - without giving me a reason as to why - and unless I replace the pipe/ boiler/ get the pipe re drilled through the wall at a different inclination he will start legal proceedings. I do not know what to do as I thought we had a soultion, plumbers can't find anything wrong, and it would be a huge expense to comply with his solutions. If anyone can help I would really appreciate it. Many thanks JM