New boiler installed by freeholder

[cuffley]

The freeholders of my building built two flats above mine in our block of flats. In doing so they had to relocate the pipework etc for my existing boiler and there was a legal agreement to replace my boiler. Ten months later I have had a number of problems with the boiler.

Whilst the boiler not working, the overflow pipe was leaking and the owner of the flats below has complained that it is affecting his property.

My plumber (investigating a leak under the sink) has also said that it has not been installed correctly and a pipe has been fitted directly into the sink waste pipe causing water to leak every time the sink is used. He says the sink carcass is rotten and I need a new kitchen and the boiler installation to be corrected.

Also in getting the original problems resolved with the boiler the boiler company (i.e. the make of the boiler rather than the company who installed it) said that there needs to be a chemical flush in order for the boiler to remain under warranty.

Should the freeholder be responsible for:

a) the repairs and/or any buildings insurance excess for the damage to the flat below

b) getting my boiler installation fixed

and
c) any replacement of the sink/worksurfaces

Also, should I be asking them to pay for the chemical flush or just paying for this?

Any advice would be good!