A Pressure Regulating Valveis avalvethat automatically cuts off the flow of a liquid or gas at a certainpressure. Regulators are used to allow high-pressurefluid supply lines or tanks to be reduced to safe and/or usablepressures for various applications.
Bosch tankless water heaters work on water pressure and flow. Some people experience fluctuating temperatures sometimes if they are on a well system as the well pump has a high and low setting for when the pump comes on and off. Most common well pumps are set to like 30 - 55 psi of pressure. So when you are using the hot water and if the pump kicks on during this time you could see a change in flow and pressure which will change the flow and water temperature out of the Bosch tankless water heater.
A Pressure Regulating Valve installed on the cold water line before the Bosch tankless water heater can be set at the low PSI such as 30 psi and then will always maintain that 30 psi consistently whether the pump kicks on or not.
There are all sorts of different pressure regulating and pressure reducing valves on the market.