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16-23 GPM Flow Switch Q12DSMSC - Bubbles Supply

16-23 GPM Flow Switch Q12DSMSC

Part #: Q12DSMSC

$192.11
In stock — ships today
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1-year warrantySame-day ship before 3pm CTPerfect Fit Guarantee30-day returns

About this flow switch

The Harwil Q12DSMSC flow switch monitors water flow in residential and commercial spa systems, triggering safety shutdowns when flow drops below 16 GPM. This 1/2" NPT threaded sensor handles up to 23 GPM maximum flow and switches 2 amp loads, making it ideal for protecting heaters and pumps from dry-fire damage. The robust design prevents costly equipment failures by ensuring adequate water circulation before allowing heating elements to activate.

At Bubbles Supply, every Q12DSMSC flow switch comes with our exact fit guarantee and ships same-day when ordered by 2 PM EST. Our 1-year warranty backs this genuine Harwil sensor, giving you confidence in long-term reliability. Professional installation recommended – verify your system's flow requirements and ensure proper threading engagement to maintain accurate flow sensing and prevent leaks.

Exact part number

Q12DSMSC

Save this for ordering or warranty claims

Also known as / Replaces

This part replaces or is interchangeable with:

  • Harwil flow switch
  • paddle flow switch
  • Q12 series flow switch
  • water flow sensor

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

Technical specifications

Amperage
2A switching capacity
Port type
1/2" NPT threaded

Plumbing notes

  • Port type: 1/2" NPT threaded

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 won't activate despite pump running
  • Spa throwing HH, ICE, or OH error codes
  • False high-limit shutdowns with adequate flow
  • Heater cycling off prematurely
  • Dry-fire protection triggering at normal flow rates
  • Spa not heating after pump replacement or replumb

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

Before you buy — quick checklist

  • Confirm your system's operating flow rate falls between 16–23 GPM — outside this range, this switch will not function correctly
  • Verify your existing flow switch is 1/2" NPT threaded before ordering
  • Check your control board's switching circuit does not exceed 2 amps — this switch is not rated for higher loads
  • Inspect the plumbing location where the switch mounts — ensure there is straight pipe upstream to allow accurate flow sensing
  • Note whether your current switch is normally open (NO) or normally closed (NC) — confirm Q12DSMSC matches your control system's wiring logic

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 Q12DSMSC flow switch
  • Mounting hardware

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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