Good afternoon, I am sorry it has taken a long time to get to you.
In answer to your query with regards to the builder, Do you have a copy of the contract stating all the stages of the work to be carried out? I take it that there is a cold water feed for the sanitaryware in the en-suite or did he miss this as well? If hehas missed this part then he would be liable under the contract to fix the issue. If it isnt on the contract then there may be no recourse to him.
This may not be helpful but read the contract and if the hot water feed was supposed to have been installed then you should bring to the attention of the builder to rectfy this as per contract. I am sorry but the work to get the pipes in would need some disruption by whoever does the job.
I hope you can get it sorted with minimum fuss., It would be a shame not to have the en-suite as planned