The 521 can be mounted in any orientation, no problem. Irregular water temperature could be caused by a number of factors. The 521 has a minimum flow rating of 1.3 GPM; flow rate less than that can cause valve "hunting" and irregular temperature fluctuations. Check valves on the hot and cold inlet are recommended to prevent cross-flow during pressure variations also. Make sure the hot water supply is delivering a good steady flow of water that is at least 25 degrees higher than the setpoint on the 521 knob.
The 521 can be mounted in any orientation, no problem. Irregular water temperature could be caused by a number of factors. The 521 has a minimum flow rating of 1.3 GPM; flow rate less than that can cause valve "hunting" and irregular temperature fluctuations. Check valves on the hot and cold inlet are recommended to prevent cross-flow during pressure variations also. Make sure the hot water supply is delivering a good steady flow of water that is at least 25 degrees higher than the setpoint on the 521 knob.