Astralpool Hurlcon Brass Plug for Hi-Limit Switches HX, JX, Viron, MX, HiNRG - also Jacuzzi
Astralpool Hurlcon Brass Plug for Hi-Limit Switches HX, JX, Viron, MX, HiNRG - also Jacuzzi is backordered and will ship as soon as it is back in stock.
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AstralPool / Hurlcon Threaded Brass Plug – 3/8" M4 with Hex Head
This genuine brass plug is used in AstralPool and Hurlcon gas heaters to accommodate high-limit (hi-limit) switches. The hi-limit sensor screws directly into this plug.
It is important to replace or repair these when leaking, and should be checked every 6-12 months. This can be one of the biggest causes of damage to gas heaters.
Suits: MX, HX, Viron, JX, ICI Heaters. Also suits Jacuzzi J-HN250C & J-HN400C heaters.
Common Issues:
These plugs can corrode over time due to poor water quality or if a small leak allows the 24V current from the hi-limit switch to create electrolytic corrosion. If the plug corrodes or leaks, it can lead to premature failure of the hi-limit switch.
Design Notes:
- Thread size: 3/8" M4
- Hex head for easy installation/removal
- Older versions had a 3/4" head and measured 13–16mm long
- Newer versions have a larger hex head and are 19–25mm long
- Fully interchangeable – just use extra thread tape and avoid overtightening
- Newer style is more robust and longer-lasting
Tip: See product photo for comparison between older and newer styles.
Installing:
Use Pink Thread Tape or a chemical-resistant thread sealant for Sealing threads. Care must be taken not to cause radial cracks in the header manifold around the female threaded area. <-- This is usually caused by over-tightening.
The red fibrous gaskets are no longer used. Use Teflon tape on the thread.
71053 old / 71060 new
Other High Limit (Hi Limit) Switches:
- 42-45C° Inlet Hi Limit (Hurlcon, Astralpool, Raypak, Pentair)
- 52-55C° Outlet Hi Limit (Hurlcon, Astralpool, Raypak, Pentair)
- 60C° Outlet Hi Limit AGS (Hurlcon, Astralpool, Raypak, Pentair)
- 70C° Outlet Hi Limit (Hurlcon, Astralpool HX/JX)
- 100C°
- 175C° Flue Temp Sensor (Hurlcon, Astralpool)
- Hurlcon / Astralpool HiLimit Locator Brass Threaded Plug
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" | 25 mm | ~33.4–33.7 mm |
| 1.5" | 40 mm | ~48.1–48.4 mm |
| 2" | 50 mm | ~60.2–60.5 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.
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).
PVC Pressure Pipe AS/NZ 1477 Dimensions1:
Common nominal sizes with typical outside diameters and indicative inside diameters by class.
| Imperial Name | Metric Name | Outside Diameter (OD) | Class 9 IDº | Class 12 IDº | Class 18 IDº |
|---|---|---|---|---|---|
| 1/2" | 15 mm | ~21.2–21.5 mm | 18.3 mm | 17.8 mm | |
| 3/4" | 20 mm | ~26.6–26.9 mm | 23.7 mm | 22.4 mm | |
| 1" | 25 mm | ~33.4–33.7 mm | 30.5 mm | 29.8 mm | 28.1 mm |
| 32 mm | ~42.1–42.4 mm | 38.5 mm | 37.5 mm | 35.4 mm | |
| 1.5" | 40 mm | ~48.1–48.4 mm | 45.2 mm | 44.1 mm | 42.8 mm |
| 2" | 50 mm | ~60.2–60.5 mm | 55.2 mm | 53.7 mm | 50.5 mm |
| 65 mm | ~75.2–75.5 mm | 68.9 mm | 67.0 mm | 63.2 mm | |
| 2.5" | ~73 mm |
- 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.
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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