Cold shower ,hot tub faucet

[Celtic]

I asked my plumber to increase the temperature of the my tub faucet and he did. However the next time I took a shower the temperature could not get above 90 . The tub faucet was 115. I took off the shower head and the temperature coming out of the shower pipe was the same as the faucet 115 . The plumber recommended a new shower head . The new shower head , a basic moen shower head same problem. Called plumber, he told me to take out the small black washer with a screen in my shower head . Did that no change in temperature still 90. Water flow rate of the new Moen showerhead 1.8. Any ideas

 

[GReynolds929]

Pictures of the valve, tub spout, and shower head would be useful. Is the tub spout and shower head controlled by the same valve? Is your water heater tank or tankless? What temp does the water reach at the sink faucet? Rest of the house?