Your question requires clarification. Is the water temperature decreasing or the amount of hot water volume? If the water temperature is decreasing in the kitchen - as well as bathroom sinks, tub, and shower, then it would be your water heater. Try increasing the temperature setting on the water heater to see if the temperature increases. If it does not increase, then your water heater element (electric) or the gas regulator may need to be replaced - or even the entire heater.
If the volume of water has decreased then you should check the hot water shut off valve under the sink. Turn the valve all the way int to completely close the valve and then open it all the way. If the valve was fully open then you may have calcium deposits from your hot water heater building up on the hot water valve under the sink and within the kitchen faucet. Turn off the water supply and disassemble the faucet as per the manufacturers instructions to clean out the valve.
If the volume of water has decreased then you should check the hot water shut off valve under the sink. Turn the valve all the way int to completely close the valve and then open it all the way. If the valve was fully open then you may have calcium deposits from your hot water heater building up on the hot water valve under the sink and within the kitchen faucet. Turn off the water supply and disassemble the faucet as per the manufacturers instructions to clean out the valve.
