I recently installed a tankless hot water heater. I have a shower panel with a single handle adjustment with a mixing valve. The only way I can get the shower hot is by restricting flow at the gate valve on the cold supply line. I have adjusted the shower anti scald valve all the way to its hottest setting. All other fixtures in house will produce hot water. I did notice in a second bathroom that has an older valve setup that when only the hot water is turned on all the way that the flow is not as strong as it used to be prior to hooking up the tankless unit. It does come out hot but the flow rate is less than if you turn on only the cold side. Could the imbalance in flow rate at the mixing valve be the reason for not getting a hot shower? Can I put a circulation pump on the hot line to increase the pressure to match that of the cold line? Do I put the pump after the tankless unit or before it? Thanks for your help.
Water pipe sizing