Some brands of pressure reducing valves (PRVs) that have been on the market for a while have a built-in bypass feature that allows increasing downstream pressure (a result of heating domestic hot water) to discharge backwards through the PRV. This "pressure relief" feature helped protect systems from overpressure damage. Most modern domestic hot water systems have expansion tanks, or methods of allowing for safe expansion, making the PRV bypass feature unnecessary. The new, high-performance 535H Series PRVs do not have a bypass feature.
March 27, 2017