Contracts and voided warranties

Jimm918

We have had a company replaces a few windows in our house a few years back and the work was split into two contracts. the front of the house was done first and was paid in full then a year later the back of the house.
When the back of the house was done we had a few issues with the company/company owner as they missed two fitting days, damaged a newly plastered wall(away from the windows) and a skylight had the wrong opaque glass fitted.

when the work was done on the second contract we asked to discuss these issues with the owner and ask if we would get any discount but he stormed out of our house. Later that night he sent us an email and said sorry as well as offering us £200 off. We accepted £100 off as we felt the rest of the work was good and it didn't warrant such a reduction.

a year later the first set of windows deveopled a fault and a few pains were changed out with no problem from the company as it was a clear manufacturing problem. 6 months later the remaining 2 pains failed in the same manner but now he has refused to replace the.

His reason is that he didnt pay the second contract in full and thus warranties for both contracts are void. (even though he offered the reduction to us as we still have the emails) He stated the previous replacements were a good will gesture but no further work could be done under warranty.

This is now going to court as we have had to get the windows replaced by another firm before they fell out.

My question is. - Can one contract effect another like this regardless of if the reductions were agreed or not?

From what I've been told and to me logically we have a fairly clear cut case as we have most of the communications in writing but i have very little knowledge of contract law and could do with the peace of mind.

Thanks in advance for any comments.