We have 2 bathrooms in the house - the main bathroom seems to have normal hot water pressure - but in our master bath the cold water pressure is very good, but once you turn on the hot water it somewhat trickles out. You can take a shower, but the water pressure very much goes down when the hot water is on. We have changed out the shower head and no improvement. Any suggestions ?

Shut the water off and open up the valve. Remove the cartridge and check and clean the inlet ports. Now turn the water back on for as moment to flush out the supplies. Reassemble and test. Better now? Tom