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1/2" MPT Flow Switch Q12DS-3-3-4S-1 - Bubbles Supply

1/2" MPT Flow Switch Q12DS-3-3-4S-1

Part #: Q12DS-3-3-4S-1

$192.11
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About this flow switch

The Harwil Q12DS-3-3-4S-1 flow switch is a precision sensor designed for spa and hot tub systems requiring reliable water flow monitoring. This 1/2" MPT threaded switch activates at 3 GPM flow rate and handles up to 1 amp electrical load, making it ideal for controlling pumps, heaters, and other spa equipment that depend on adequate water circulation for safe operation.

Built to OEM specifications, this genuine Harwil flow switch delivers the exact fit and performance your spa system demands. At Bubbles Supply, we guarantee precise fitment and back every sensor with our comprehensive 1-year warranty. Most orders ship same day, getting your spa back online fast. When installing, ensure proper thread sealant on the 1/2" MPT connection and verify electrical connections match your system's requirements for optimal performance and safety.

Exact part number

Q12DS-3-3-4S-1

Save this for ordering or warranty claims

Also known as / Replaces

This part replaces or is interchangeable with:

  • 1/2 inch MPT flow switch
  • 3 GPM flow switch
  • Harwil Q12DS flow switch

Looking for an older part number? Check our supersession lookup tool

Technical specifications

Amperage
1A max
Port type
1/2" MPT (Male Pipe Thread) inline

Plumbing notes

  • Port type: 1/2" MPT (Male Pipe Thread) inline

Need help measuring? Email hello@bubblessupply.com with a photo of your existing plumbing.

Common symptoms this part fixes

If your spa is showing any of these signs, this part is likely your fix:

  • Heater not activating despite pump running
  • Spa throwing HH, ICE, or OH error codes
  • Heater cycles off prematurely
  • Spa control board not detecting water flow
  • Equipment running dry due to missed low-flow condition

Not sure if this is your problem? Try our diagnostic centre or .

Before you buy — quick checklist

  • Confirm your existing flow switch uses 1/2" MPT threading — not barb, compression, or slip fit
  • Verify your system triggers at 3 GPM — some systems require a different activation threshold
  • Check that your control board circuit draws no more than 1 amp through the switch contacts
  • Inspect the switch housing in your equipment bay for thread orientation and clearance before ordering
  • Note whether your current switch is SPST or SPDT — confirm this unit matches your wiring configuration

Reading the checklist now prevents 90% of returns. Worth the 60 seconds.

Install difficulty: Medium — Some experience neededTypically 30–60 minutes

What's in the box

  • Harwil Q12DS-3-3-4S-1 flow switch
  • Mounting hardware (if included by manufacturer)

If your order is missing any items listed above, contact hello@bubblessupply.com within 48 hours of delivery.

Warranty

1 year manufacturer warranty against defects

Covers manufacturing defects. Does not cover improper installation, normal wear, or accidental damage.

Warranty claims: warranty@bubblessupply.com

Perfect Fit Guarantee

Ordered with our help and the part doesn't fit? Contact us before installation. We'll resolve it with an exchange, replacement recommendation, or return approval.

Learn about our Perfect Fit Guarantee →

Shipping

We ship across the US and Canada. US orders ship from our US warehouse to US customers; Canadian orders ship from our Canadian warehouse to Canadian customers — no cross-border shipping, no surprise duties. In-stock orders placed before 3pm CT ship same day. Standard shipping $9.95 flat rate. Free shipping on orders over $200. Express options available at checkout.

Returns

30-day hassle-free returns on unused parts in original packaging. Contact us before returning to receive your RMA number.

Frequently asked questions

Check the Compatibility section above to confirm fitment for your spa brand and model. If your model is not listed, use our fitment selector at /pages/find-my-part or ask our parts AI for a personalized recommendation.

In-stock orders placed before 3pm CT ship the same day. You will receive tracking information by email as soon as your order ships.

We accept returns within 30 days of delivery for unused items in original packaging. Email returns@bubblessupply.com with your order number to start a return. Installed electrical parts cannot be returned for safety reasons.

Yes, all new parts come with a 1-year warranty against manufacturing defects. Warranty does not cover damage from improper installation or normal wear and tear.

Customer reviews

AI Fitment Assistant

Tell us your spa model and we will confirm this part fits before you buy.

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