We got a new hot water tank installed yesterday. Since the water was turned back on all was well until this morning. The kitchen faucets have a pressure difference in the hot and cold. (single tap mixer) To the right (cold) the pressure is fine, but to the left (hot) the pressure is low. We have already replaced the cartridge to see if it was that, but it is the same problem with the new cartridge. What could the problem be?

Did you flush the faucet before installing the new cartridge, if not close the angle valve under the sink remove the cartridge open the valve for a few seconds just to flush the debris, install the cartridge and check should be OK, good luck.

John

You could have some debris in angle stop, water supplies and / or inlets into the faucet.

Do this:
Close one angle stop. Unscrew water supply line. Put towel over angle stop and slowly open it. See if you get good pressure. Repeat with other angle stop. If positive, than remove water supply line and see if it is clear of debris. Repeat with other water supply. If clear, than take a flash light and look upwards into the facet connector lines and look for debris. If blocked, take wire and clean it. That should do...

Yep Milo is correct follow his instructions and you will be Ok, Thanks.

John