Is it makruh (disliked) to pour boiling or freezing water over the body during wudu?
If the water is so hot that it becomes difficult for the completion of the sunnan of wudu, then this is considered makruh. This is also the case for water which is too cold and does not allow the completion of the sunnan to take place. However, if the water is such that is prevents the completion of a compulsory act of wudu then this will be considered unlawful and such a wudu will not be valid.
And Allah ﷻ knows the best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk