For best practice

and Luxaire models like the DF090N10N2AAA3A

System Reliability: Helps maintain correct static pressure within the combustion chamber

it is best practice to mount the valve with the solenoid vertical and upright to prevent sediment from settling in the core tube and causing erratic operation

Watts 0556050 Valve 318973-401 For best practiceThe Watts 0556050 (Series LF4L) is a high performance 3 4 inch pressure relief valve specifically engineered for tankless water heaters and domestic storage tanks. Featuring a lead free copper silicon alloy body, this poppet type valve is designed to mitigate excessive pressure risks in residential and commercial plumbing systems. It arrives factory set at 150 psi and features a durable stainless steel spring and silicone disc to ensure a tight seal