and that the blower is creating sufficient negative pressure to pull the valve diaphragm open

including the popular S4A

For flow switch troubleshooting or fine-tuning

Durable Construction: Features stainless steel components to resist corrosion and thermal fatigue in demanding environments

OEM Compatibility: Genuine York HVAC parts guarantee proper fitment and electrical specifications

Watts 0259705 Valve 320735-701 and that the blower isThe Watts 0259705 is a high capacity 1 inch temperature and pressure relief valve engineered for commercial water heating systems and storage tanks. This Series 140X valve is designed to provide automatic protection against excessive thermal expansion and pressure spikes. Featuring a bronze body construction and an extension thermostat with a 6 inch probe, it ensures accurate sensing of tank temperatures up to 210F. The unit is ASME rated and CSA