Astralpool Hi Limit 52C - NC Auto
Astralpool Hi Limit 52C - NC Auto - is backordered and will ship as soon as it is back in stock.
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Don't Guess - Ask Us!
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Astralpool Hi Limit 52C - NC Auto
Astralpool Hi Limit 52C - NC Auto - is backordered and will ship as soon as it is back in stock.
Astralpool
Hi Limit 52°C – NC Auto Thread. 52-55C high limit switch suits all MX, HX, JX, HiNRG, Viron, ICI gas heaters. High Limit Switch used in Hurlcon & Astralpool gas heaters and INSNRG gas heaters. Common source of F2 error. Used on many pool and spa heaters. Part Number 71031 and 21C01513001. Last photo shows the high limit screwed in the brass plug.
The most common reason for failure is a leaking brass plug causing the limit switch to corrode.
Note: We are that some online sellers are illegally selling low-quality unapproved cheap switches that are non-compliant. All hi-limit switches must have DVE certification (ours do).
These suit all Hurlcon Astralpool HX, MX, Viron, HiNRG, JX Gas Heaters. Also suits Jacuzzi J-HN250C & J-HN400C heaters and INSNRG.
Pick Up Available, or Fast Shipping.
Found on the Outlet side of a gas pool or spa heater heater. Also called a Thermal Cutout or Thermal Safety Cutout Switch.
Failed hi limits can cause the F2 Errors found on Hurlcon and Astral Gas Heaters. Commonly fail due to condensation and leaks. Should be replaced every few years as part of preventative maintenance.
Both Inlet & Outlet hi limits should be replaced at the same time.
There are two types, threaded (Viron, HiNRG, later HX, JX, MX) which is screwed into the brass plug, and non-threaded style that is held in either by a bracket (older MX), or screws (older JX, HX).
Important Notes & Installation:
- AstralPool / Hurlcon gas heaters have a separate brass plug that this hi-limit screws into. Check the brass plug for leaks, corrosion, or damaged threads, and replace it if necessary. The last images show the hi-limit screwed into the brass plug for reference.
- On older heaters, corrosion often makes these two separate parts look like one single piece with a larger thread. They are not one piece even if it looks like it us! It is a hi-limit switch screwed into a separate brass plug -- See images.
- These are an Extremely Important Safety feature found on heaters, and are required by law. They must be replaced when necessary.
- Most new high limits and all Non-threaded and Aftermarket switches use more common 6.3mm spade terminals (available as an Add-on in this listing or at any electrical supplier).
- Some brass plugs are not tapped as deeply as others. If the new hi-limit does not gently screw all the way in, carefully file a small amount off the M4 thread on the new switch.
- Do not overtighten. The thin brass M4 thread is extremely easy to break. If you feel any resistance when screwing it in, stop, clean the threads, and apply a small amount of light lubricant. Broken threads are not covered by warranty.
- This hi-limit is for the outlet side of the water connection. Inlet hi-limits are listed below.
Hurlcon AstralPool Jacuzzi:
- HX 70, HX 120, HX 150, MX 150, MX 200, MX 250, MX 300, MX 350, MX 400, MX 500, JX 130, JX 160, HiNRG 175, HiNRG 250, HiNRG 400, Viron 250, Viron 350, Viron 450, Viron 550, WX 70, WX 120, WX 150, ICI 200, ICI 400, Jacuzzi and many more.
- Campini Ty60 10/250 T210 41-04 55°C
High Limit (Hi Limit) Switches:
- 42-45C° Inlet Hi Limit (Hurlcon, Astralpool)
- 52-55C° Outlet Hi Limit (Hurlcon, Astralpool)
- 70C° Outlet Hi Limit (Hurlcon, Astralpool)
- 175C° Flue Temp Sensor (Hurlcon, Astralpool)
- Hurlcon / Astralpool HiLimit Locator Brass Threaded Plug
Manufacturer Catalogues, Diagrams & Part Numbers
Need exploded views, spare part numbers, product numbers, diagrams, or more product information? See the manufacturer catalogues: AstralPool Catalogue 2026 | Zodiac Catalogue 2026
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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55° Threaded + 2x Red Spade Female Terminals