Mercury is supposed to be combust if Margi Mercury is within 14 degrees from the Sun; but if it retrograde it should be within 12 degrees from the Sun.
But late Bipin Behari had taken the view that Mercury is the only planet which not deemed combust despite its extreme nearness to the Sun.
We may also mention that it is believed- When Budha is in rapt conjunction with Ravi he gives excellent results.
According to Varahamihira, if the Sun is conjunct with Mercury,the person shall be skillful, intelligent, renowned and happy.
Saravali of Kalyan Varma indicates that Mercury conjunct with the Sun makes one a good subordinate, gives fluctuating riches, makes him soft spoken, treating good name as his wealth, respected, favoured by the authorities, best among the righteous, wealthy, strong and good featured.
Sri Gauri Sidering Budhadityahankar kapoor advised to take nearness 3 degree to Ravi as real combustion.
dr. B.V.Raman, while considering Budha-Aditya Yoga observed” If Mercury combines with the Sun,” it makes a person “Highly intelligent, skillful in all works, good reputation, personal respect and surrounded by all comforts and happiness.
Accepting that possibly Mercury was an exception to the rule that on combustion every planet looses its power to do good. But he insisted that Mercury should not be within 10 degrees of the Sun to give rise to Budha-Aditya Yoga.