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3/4" MPT Flow Switch Q12N50 - Bubbles Supply

3/4" MPT Flow Switch Q12N50

Part #: Q12N50

$100.43
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About this flow switch

The Harwil Q12N50 3/4" MPT flow switch is a precision sensor designed for spa and hot tub circulation systems. This normally open (NO) flow switch monitors water flow through your spa's plumbing, automatically shutting down heaters when flow drops below safe levels to prevent costly damage from dry-fire conditions.

Built with 3 SM specifications and featuring a durable 6-foot lead wire rated for 1/2 amp switching capacity, this OEM-quality sensor delivers reliable performance in demanding spa environments. The 3/4" male pipe thread connection ensures secure installation in standard spa plumbing configurations. At Bubbles Supply, we guarantee an exact fit for your application, ship same-day from our Canadian warehouse, and back every sensor with a full 1-year warranty. Professional installation recommended to ensure proper flow rate calibration and optimal heater protection.

Exact part number

Q12N50

Save this for ordering or warranty claims

Also known as / Replaces

This part replaces or is interchangeable with:

  • 3/4 MPT flow switch
  • Harwil flow switch
  • hot tub flow switch
  • Q12N50 flow switch
  • spa flow sensor

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

Technical specifications

Amperage
0.5A switching capacity
Port type
3/4" Male Pipe Thread (MPT) inline

Plumbing notes

  • Port type: 3/4" Male Pipe Thread (MPT) 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 turning on
  • Spa displaying HH, ICE, or OH error codes
  • Heater shuts off intermittently during normal operation
  • Spa goes into high-limit lockout with adequate water flow
  • Circulation pump running but heater won't engage

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

Before you buy — quick checklist

  • Confirm your existing flow switch uses 3/4" MPT (male pipe thread) — not female or barbed fittings
  • Verify your control board or heater circuit is rated for a normally open (NO) flow switch configuration
  • Check lead wire length — this switch ships with a 6-foot lead; confirm it reaches your control board without splicing
  • Inspect the plumbing port where the switch installs for damage, corrosion, or stripped threads before ordering
  • Confirm the fault code on your spa (HH, OH, ICE) is actually flow-related and not a failed temp sensor or clogged filter

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 Q12N50 flow switch
  • 6-foot lead wire (pre-attached)
  • Installation hardware (if included by manufacturer — verify on receipt)

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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