I replaced the hot water heater in my house on my own since I couldn't afford a new heater and someone to install it and I have done this before. This time after I installed the hot water heater the pressure in both my bathrooms went so low that not much you can do with it. Kind of comes out with good pressure for the first second then dies and the pressure just drops.. any advice? This is only for the hot water and mainly the pressure for both bathrooms bathtubs.

Oh and I forgot and its only the hot water, the cold water seems to flow the same.

Do you have good pressure on the lav faucets? And kitchen faucet? Did you install a new shutoff valve on the supply to water heater? If not then it may be the valve that may have froze partially on the off position. Need to check it out.

I agree with Truck, I would look at the cold water shut off valve. Especially if you did any soldering upstream of the valve. Excess solder in a joint can flow inside and solidify unattached, then flow to next valve port and block it. Valves are cheap, suggest that you just replace it.

Hey guys thanks for the help. I did install new valves and the flow to all the house is fine just when I open the shower or bathtub hot water that the pressure just isn't enough.

Possible debris in the tub and shower valve. Remove hot water stem and flush.