Is a man considered to be remiss for delaying the Dhuhr prayer and combining it with Asr due to the hardship of waiting for water to heat up, knowing that combining prayers without an excuse is one of the major sins?

Allah Almighty commanded His servants to establish prayer at its specified times, and it is not permissible to delay or combine them except for an excuse such as travel or illness. Whoever prays before the time intentionally is sinful and must repeat the prayer. And whoever delays it intentionally without an excuse is sinful, and his prayer is not accepted according to the most authoritative opinion. It is permissible to combine prayers while at home (not traveling) to alleviate hardship, as the Prophet (peace be upon him) combined Dhuhr and Asr, and Maghrib and Isha in Medina without fear or rain, so as not to cause hardship for his Ummah. And whoever faces hardship in performing it, such as extreme fatigue where there is a fear of missing the time, it is permissible for him to combine prayers either by advancing or delaying them.