Tecmark Hydroquip Adjustable Pressure Switch - Universal - 1/8" NPT - 3902 3903

Tecmark / Hydroquip Spa Heater Pressure Switch replaces 3903-DF, 3902, 3903, 34-0178 1 Amp SPST for spa equipment and heaters. This is a very common pressure switch used by Balboa, Gecko, Davey, Spa-Quip, Spa Builders, HydroQuip, Pentair and others. Usually found near the heater assembly. They were originally branded as Tecmark, but may also be labelled Hydroquip now.

Details:

• 1-5 psi 7-35kpa adjustable SPST 
• Found in a large number of spa and pool heaters
• On/Off device that controls heater operation
• Utilises a diaphragm to sense water pressure. This closes a switch.
• 1/8" NPT Thread rated to 1A. Fits most spa electric heaters.
• Has two Spade connectors
• 3902 and 3903 are interchangeable in spa applications. 

Variant and Other Information:

• 3902 1A, 1-5PSI Adjustable, 1/8" NPT
• 3903 1A, 1A, 1-5PSI Fixed by glue @ 1.5PSI, but Adjustable, 1/8" NPT w/o Screws
• WWDG is rebranded 390x 3A version.
• -DF has terminal screws in addition to spade connectors.
• -BP is a 3A variant. Some were actually still 1A though. Go figure!
• 99% of spa applications do not require adjustment from factory.
• These have been rebranded by some other companies over the years.

Basic Installation Instructions:
(To be performed by an Electrically-Qualified Person)

1. Preparation:

• Turn off power at the mains before beginning installation.
• Apply thread tape or sealant to the switch threads.
• Hand-tighten the switch until snug—do not use tools to avoid over-tightening.

2. Initial Testing & Adjustment:

• Using a multimeter, check the switch’s status before turning the power on:
  • It should read Open-circuit (no electrical continuity) when the system is off and no pumps are running.
  • If the switch is Closed-circuit (showing continuity), adjust the screw on the switch until it reads Open-circuit.
  • Turn the switch slightly further in to prevent excessive sensitivity.
    

3. Power-On Testing:

• Turn the power on and check the switch function:
  • The switch should be Closed-circuit when the pump is running.
  • It should return to Open-circuit when the pump turns off.
  • Repeat the test to confirm proper operation.

4. Note:

• Dirty or clogged filters can restrict water flow, causing the switch to open unexpectedly. Ensure filters are clean for proper function.

Part Numbers & Descriptions This Replaces: 

3902 - 1Amp, 1-5psi Adjustable, 1/8" NPT 3903 - 1Amp, 1-5psi Adjustable, 1/8" NPT3903-BP 3Amp, PSI Factory Set Non-Adjustable, 1/8" NPT 3903-DF 1Amp, 1.5psi fixed, 1/8" NPT, MH26414, 3903-EECS, A2F / 0517, 34-0178, 3900, 3901, 3903, 3904, 3906, 3909, PRS-1100, PRS-1101, M3218, 71076, 26775, 26776, 26778, R-113, R-130, R-132B, S-1921173328, B600025, 600025,