If he wakes up late and the water is cold, can he do tayammum?
Question

A man became junub as the result of an erotic dream, and he was late for work, and it was raining and cold, so he did tayammum with clean earth. Is it permissible to do that? Please note that he was afraid of being late for work and he was also afraid that he might become sick or die (if he bathed in cold water).
Praise be to Allah.If a person has an erotic dream and emits maniy (semen), he has to do ghusl so that he can pray, and it is not permissible for him to do tayammum instead unless there is no water available or he fears that he may be harmed as a result of using it, because Allah says (interpretation of the meaning): 
“O you who believe! When you intend to offer As-Salaah (the prayer), wash your faces and your hands (forearms) up to the elbows, rub (by passing wet hands over) your heads, and (wash) your feet up to the ankles. If you are in a state of Janaaba (i.e. after a sexual discharge), purify yourselves (bathe your whole body). But if you are ill or on a journey, or any of you comes after answering the call of nature, or you have been in contact with women (i.e. sexual intercourse), and you find no water, then perform Tayammum with clean earth and rub therewith your faces and hands” [al-Maa'idah 5:6]
 And the Prophet (peace and blessings of Allah be upon him) said: “Clean earth is the wudoo’ of the Muslim even if he cannot find water for ten years, but if he can find water, then he should fear Allah and let it touch his skin, for that is better.” Narrated by al-Bazzaar, and classed as saheeh by al-Albani in Saheeh al-Jaami’, no. 3861. 
If a person wakes up junub and is afraid that he will be harmed by using water because the weather is cold, and he can heat the water, he must do that, even if the time for the prayer ends, because the sleeper is excused, and the time for him is when he woke up, so prayer is binding for him, along with whatever is required of purification.  
But if he has no means of heating the water, it is permissible for him to do tayammum in that case. 
Fear of being late for work is not regarded as an excuse that makes it permissible not to do ghusl and to do tayammum instead. 
The one who does tayammum with no excuse that makes tayammum permissible has to repeat the prayers that he offered with that tayammum, so that he will discharge his duty. 
The Standing Committee for Issuing Fatwas was asked: If it is very, very cold and the water in the vessel or jug is freezing, and the person has become junub, for example, and the water will affect him and give him a fever, then what should he do? 
They replied: 
If the matter is as described, then he may do tayammum. Allah says (interpretation of the meaning): 
“But if you are ill or on a journey, or any of you comes after answering the call of nature, or you have been in contact with women (i.e. sexual intercourse), and you find no water, then perform Tayammum with clean earth and rub therewith your faces and hands”
[al-Maa'idah 5:6]
But if it is possible to heat it with fire and the like, then he must do ghusl, because Allah says (interpretation of the meaning): 
“So keep your duty to Allah and fear Him as much as you can” [al-Taghaabun 64:16]
End quote. 
And Allah knows best.