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,
