A copper press joint is only as good as the O-ring inside it. The copper does the mechanical work, but the seal is what keeps water in — and different seal materials are rated for very different temperatures. Choose the wrong one on a solar collector circuit and the joint can be fine on day one and weeping a few seasons later.
The two seals in the Standard Press range
| Standard water fittings | Solar (high-temp) fittings | |
|---|---|---|
| Seal material | EPDM, black | FKM (Viton), red |
| Temperature rating | Up to 120°C | −20°C to +170°C |
| Max working pressure | 1600 kPa | 1600 kPa |
| Press profile | V-profile | V-profile |
| Typical use | Potable hot and cold water | Solar collector circuits, high-temp hot water service pipework |
Both ranges are manufactured to AS 3688 and use AS 1432 Type A or B copper tube. The pressing process and tooling are the same — the difference is entirely in the seal.
Why temperature matters to a seal
An O-ring seals because it's squeezed and pushes back against the tube and fitting. Run a seal above its rated temperature for long enough and it hardens and loses that push-back (known as compression set). The joint doesn't fail dramatically; it slowly loses grip and starts to weep. That's why the rating matters more for the hottest sustained conditions on the line than for the normal operating temperature.
Where the red FKM seal is worth it
- Solar collector circuits: roof collectors can stagnate (sit full and sun-baked with no flow) at temperatures well beyond normal hot water service. This is the clearest case for FKM.
- Collector connections and roof penetrations on solar hot water, where the pipe sees the collector's temperature directly.
- The hot side of high-temperature storage systems, or anywhere the system designer or manufacturer specifies a higher seal rating.
Where standard EPDM is fine
Ordinary hot and cold potable water services sit well inside the 120°C EPDM rating. Most heat pump flow and return lines also run at normal hot water temperatures, so standard fittings are generally within rating — the FKM solar range gives extra margin where the heat pump manufacturer or the job spec calls for it. Using solar fittings on a normal water line doesn't hurt anything; it just costs more than it needs to.
The solar range at PSA
The high-temperature press range covers the shapes you need on a collector run, 15mm to 25mm:
- Solar Coupling (CUS.21) — $4.35 / $6.55 / $9.00
- Solar 90° Elbow (CUS.31) — $5.02 / $8.69 / $20.55
- Solar Equal Tee (CUS.51) — $8.74 / $13.95 / $21.10
- Solar Male Adaptor (CUS.74) — 15 x 1/2", 20 x 3/4", 25 x 1" BSP
- Solar Female Adaptor (CUS.73) — 15 x 1/2", 20 x 3/4", 25 x 1" BSP
Don't mix them up on site
The red seal is visible at the socket mouth, so solar fittings can be identified on the shelf and in the installed pipework. Keep solar stock in its own bin on the van. The most common mistake isn't choosing the wrong range on paper — it's grabbing a black-seal fitting out of the wrong bag halfway through a collector run.
Not suited to steam or anything outside hot water service pipework — check with our team before ordering for unusual applications. For standard water work, see the main copper press water range, and for gas work see why water and gas press fittings aren't interchangeable.
Frequently Asked Questions
What temperature are standard copper press fittings rated to?
Standard Press water fittings with black EPDM seals are rated up to 120°C at up to 1600 kPa. The solar range with red FKM (Viton) seals is rated from −20°C to +170°C.
Can I use standard copper press fittings on solar hot water?
Not on the collector circuit. Collectors can stagnate at temperatures beyond the EPDM rating, so use FKM-sealed solar fittings there. Standard fittings remain suitable on normal-temperature hot and cold water lines.
How do I tell a solar press fitting from a standard one?
Look at the socket mouth. Solar fittings have a red FKM seal; standard water fittings have a black EPDM seal.
Do solar press fittings need a different press tool?
No. They're V-profile like the standard water range, so the same V-profile jaws and tool are used.