Hi looking for constructive advice. Recently had back boiler replaced with a combo boiler. Noticed pressure dropping, installer came out and found leak where it was capped off in fire place. Later found additional leak from compression joint below pipe where a TRV had been fitted which I put down to the movement off fitting TRV (water leaked through ceiling). Installer came out replaced some pipe work in fire place and replaced a compression joint with soldered joint with new pipe to TRV. Happy days until I was sent a bill for this work when queried told replacing old pipe work not part of the original work. My uneducated opinion is these are issues part of the install, in my line of work a contingency budget for unexpected costs is factored in to quote. have I got this completely wrong and should just pay up? many thanks.