1st make sure the valves are on all the way. The valves may be old also. Make sure there are no kinks in the supply line. Once that is verified and still a flow issue remove supply lines (turn valves off prior) to check for debris in the line. With the supply lines off then turn the faucet on to the warm position and blow it out as there may be debris in the faucet. You also may have a calcium build up in the head. Clean it with some diluted CLR.
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1st make sure the valves are on all the way. The valves may be old also. Make sure there are no kinks in the supply line. Once that is verified and still a flow issue remove supply lines (turn valves off prior) to check for debris in the line. With the supply lines off then turn the faucet on to the warm position and blow it out as there may be debris in the faucet. You also may have a calcium build up in the head. Clean it with some diluted CLR.