SpaNET SV2, SV3, SV4 Optical Water Sensor and Thermistor Assembly
SpaNET SV2, SV3, SV4 Optical Water Sensor and Thermistor Assembly is backordered and will ship as soon as it is back in stock.
Don't Guess - Ask Us!
Don't Guess - Ask Us!
Not sure if it’s the right part? Send us a message and a photo of what you’re replacing, or what you need, and we’ll help make sure you get the right part the first time.
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Delivery and Shipping Info*
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SpaNET SV2, SV3, SV4 Optical Water Sensor and Thermistor Assembly
SpaNET SV2, SV3, SV4 Optical Water Sensor and Thermistor Assembly is backordered and will ship as soon as it is back in stock.
SpaNET SV2, SV3 & SV4 Optical Water Sensor and Thermistor Assembly to suit SV Series heater tubes (V1 & V2 models). This complete heater sensor assembly includes the optical water sensor, thermistor, clear plastic housing, and O-ring.
This is a common replacement part on SpaNET SV systems when a spa is showing Water Prime, heater sensor, or unstable temperature-related faults. It is also a known leak point on some spas, particularly where water balance has been poor or the sensor well has deteriorated over time.
Where there is corrosion around the sensor, we recommend replacing the entire heater assembly (here).
We keep these physically in stock for fast shipping or local pick-up, unlike most drop-shipping websites.
Common symptoms this part may relate to
- Water Prime errors
- Heater Sensor errors
- Incorrect or unstable temperature readings
- Temperature display stuck on 99.9°
- Visible leaking from the heater sensor area
Common SpaNET fault codes associated with sensor or water flow issues
- ER-2 - Heater sensor fault / heater sensor connection issue
- ER-3 - Water Prime / insufficient water flow or air detected in heater tube
- ER-5 - Over-temperature / abnormal temperature reading condition
- Temperature reading of 99.9°
Important: Fault codes can have more than one cause. Dirty filters, low water level, airlocks, pump problems, damaged plugs, and corroded sensor wells can produce similar symptoms. Replacing the sensor will not fix every spa with these errors.
Compatibility
- Suits SpaNET SV Series control systems with the square plug
- Suits: SV2, SV3, SV4
- Suits: SV Series heater tubes V1 and V2
- Does not suit: XS Series
- Does not suit: SV Mini
What is included
- Optical water sensor and thermistor assembly
- Clear plastic housing
- O-ring
Installation notes
- Use a small amount of silicone lubricant on the O-ring during installation
- Inspect the sensor well carefully before fitting the new part
- If the sensor well is corroded, pitted, cracked, or leaking, the new sensor may also leak or fail prematurely
- Always isolate power before carrying out inspection or replacement
Common cause of failure
Low pH, poor water chemistry, and long-term corrosion are common reasons these assemblies leak or fail. If water balance has been neglected, inspect surrounding heater components carefully before ordering and fitting replacement parts.
Please check before ordering
This part is for SpaNET SV2, SV3 and SV4 systems only. Please check the plug style, controller model, and heater configuration carefully before purchase. If you are unsure, send us clear photos of your spa pack, heater tube, plug, and the old sensor assembly so we can help identify it correctly.
In plumbing, named sizes are not the actual measurements. A pipe called “50mm” or “2"” does not measure 50 mm across. Instead, it follows nominal sizing, an internationally-standardised naming system.
Use the Outside Diameter (OD) to check your pipe against fittings. Below is a quick reference for common spa & pool pipe sizes:
| Imperial Name | Metric Name | Pipe Diameter (OD) |
|---|---|---|
| 1/2" | 15mm | ~21.2–21.5 mm |
| 3/4" | 20mm | ~26.6–26.9 mm |
| 1" | 25 mm | ~33.4–33.7 mm |
| 1.5" | 40 mm | ~48.1–48.4 mm |
| 2" | 50 mm | ~60.2–60.8 mm |
| 2.5" | 65 mm | ~75.2–75.5 mm |
These are nominal sizes and are designed to fit matching fittings — not to measure exactly what their name suggests. These are based on PVC Pressure Pipe AS/NZ 1477 Dimensions1.
- º Internal diameters vary slightly by manufacturer and class.
- 1 Not all pool/spa fittings match these dimensions exactly. Some do not follow Australian or international standards. Chinese spas may use proprietary fittings.
Understanding Plumbing Sizes & Nominal Measurements
Plumbing sizes can be confusing. PVC and many other pipe systems use nominal sizes—the size is a name, not the exact measured dimension. This convention is used across most pool and spa systems so that pipes and fittings remain compatible.
Why pipe sizes don’t match the measurements
The Nominal Pipe Size (NPS) system standardises pipe dimensions so that pipes, fittings, valves, and accessories interoperate. Plumbers work with these nominal names every day, but DIYers can be tripped up if they try to match by a tape-measure alone.
How to Measure Pipe Correctly
-
Pipe size is identified by:
- The pipe’s Outside Diameter (OD).
- The fitting’s Inside Diameter (ID) (socket opening).
- Pipe Class / Schedule (e.g., Class 9, 12, 18 or Sch 40) relates to wall thickness and therefore the Internal Diameter (ID) and pressure rating.
- The outside diameter of a fitting is not useful (wall thickness varies by manufacturer).
Hose & Tube Dimensions
Common flexible hose sizes used in pool/spa systems (approximate IDs).
| Imperial Name | Metric Name | Inside Diameter (ID) |
|---|---|---|
| 3/8" | 9–10 mm | ~9 mm |
| 3/4" | 19 mm | ~19 mm |
BSP – British Standard Pipe Thread Sizes
BSP thread names are also nominal. The thread OD will not equal the nominal name.
| BSP Thread Size Naming | Outside Diameter (mm / inch) | TPI |
|---|---|---|
| 1/16" BSP | 7.7 mm / 0.304" | 28 |
| 1/8" BSP | 9.7 mm / 0.383" | 28 |
| 1/4" BSP | 13.16 mm / 0.518" | 19 |
| 3/8" BSP | 16.66 mm / 0.656" | 19 |
| 1/2" BSP / 15 mm | 20.99 mm / 0.825" | 14 |
| 5/8" BSP | 22.99 mm / 0.902" | 14 |
| 3/4" BSP / 20 mm | 26.44 mm / 1.041" | 14 |
| 7/8" BSP | 30.20 mm / 1.189" | 14 |
| 1" BSP / 25 mm | 33.25 mm / 1.309" | 11 |
| 1-1/4" BSP | 41.91 mm / 1.650" | 11 |
| 1-1/2" BSP / 40 mm | 47.80 mm / 1.882" | 11 |
| 2" BSP / 50 mm | 59.61 mm / 2.347" | 11 |
| 2-1/4" BSP | 65.71 mm / 2.587" | 11 |
| 2-1/2" BSP | 75.18 mm / 2.960" | 11 |
| 3" BSP | 87.88 mm / 3.460" | 11 |
| 4" BSP | 113.03 mm / 4.450" | 11 |
| 5" BSP | 138.43 mm / 5.450" | 11 |
| 6" BSP | 163.83 mm / 6.450" | 11 |
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