Im assuming that this is an install that you have done for the builder. If so It sounds to me like you've answered your own questions here.
1. Decoupling was agreed but not supplied so thats a breach of contract.
2. You guaranteed the tiles would not fail as a result and they have failed somthats a breach of guarantee.
3. The floor was clearly wet and probably too wet to tile directly. I'm assuming no moisture test done which is a failure to observe due diligence.
4. The underfloor heating was not commissioned prior to tiling which fails to meet the required standard of best practice.
5. Plaster left on the floor prior to tiling shows lacking adequate preparation which is also a failure to meet the required standard if best practice.
If I were you i'd be doing everything reasonable to sort it out. Ie. Lift and replace the tiles at your cost. If it went to litigation you would not have a leg to stand on. It would not be diffucult for the builder to prove to a court that it is your fault regardless of what temperature the heating went on at.
1. Decoupling was agreed but not supplied so thats a breach of contract.
2. You guaranteed the tiles would not fail as a result and they have failed somthats a breach of guarantee.
3. The floor was clearly wet and probably too wet to tile directly. I'm assuming no moisture test done which is a failure to observe due diligence.
4. The underfloor heating was not commissioned prior to tiling which fails to meet the required standard of best practice.
5. Plaster left on the floor prior to tiling shows lacking adequate preparation which is also a failure to meet the required standard if best practice.
If I were you i'd be doing everything reasonable to sort it out. Ie. Lift and replace the tiles at your cost. If it went to litigation you would not have a leg to stand on. It would not be diffucult for the builder to prove to a court that it is your fault regardless of what temperature the heating went on at.
