After having a new water heater installed by Lowe's the hot water is overridden by the cold water in the shower,the hot water can be full blast and as soon as the cold is turned on just a little it is cold ?

Do you have similar issues at other spigots and faucets, if so call Lowe's back out.

I agree with ballengerb1. Call back Lowe's.

Had same problem with my new install. Thermostat was set too low.

Chuck