The 3903‑BP pressure switch from Tecmark (also sold under part numbers like 5‑20‑0008, TDI3903BP) is a simple, reliable safety‑related component used in spa and hot tub control systems. It monitors water pressure in the heater or plumbing system and sends an electrical signal when the correct pressure (flow) is present, helping the control board manage heater operation safely.

• Tecmark 1‑5 PSI 1/8″ NPT Pressure Switch – 3903‑BP
• Reliable Flow/Pressure Detection — Converts water pressure into an electrical trigger so the heater or control system only activates when sufficient flow/pressure exists.
• 1‑5 PSI Set Point — Factory‑set at approximately 1.5 PSI and not adjustable; ideal for standard spa applications.
• 1/8″ NPT Connection — Standard male pipe thread fits directly into heater pressure switch ports or 1/8″ tapped plumbing.
• SPST Switch Type — Single pole, single throw configuration commonly used in spa safety circuits.
• 3 Amp Rated — Supports up to 3 amps of control load for typical spa control board connections.
• Durable Construction — Plastic threaded body and internal diaphragm designed for long life in hot, wet environments.
• Part No.: 3903‑BP

Why choose this product?
This pressure switch is an essential safety component for spa heater systems. Replacing a faulty switch restores proper pressure/flow detection, prevents heater dry‑fire conditions, and helps ensure efficient and safe operation of your spa equipment.