We Replumbed Our Entire Boat… And It Leaked Everywhere
We rebuilt the entire fresh water system with PEX. Then we pressure tested it. Seven days and ten hardware store trips later, here's what we learned.
he fresh water system was completely rebuilt — nearly 200 feet of PEX-A pipe run through both hulls, hundreds of fittings installed, expansion sleeves stretched and seated. The entire system was closed up and ready for pressure testing. The plan was simple: rent a small air compressor, pressurize the system, fix a couple of leaks if any showed up, and cross it off the list. One day, maybe two.
It took seven days. Ten trips to the hardware store. Countless fittings cut off and replaced. And by the end, the system was still losing pressure somewhere they couldn't find.
This episode is what happens when confidence meets reality in a boat refit.
📺 Watch Episode 66 👉
Seven days. Ten hardware store trips. Countless fittings replaced. Here's what actually happens when a PEX plumbing system doesn't go as planned.We rebuilt the entire fresh water system with PEX. Then we pressure tested it. Seven days and ten hardware store trips later, here's what we learned.
What Happened
Day one started with optimism. The rented pancake air compressor was hooked up through a pressure gauge rigged to the steam oven water connection. Air went in. Pressure started building. Then the leaks started showing up. Not just a couple. Dozens.
Soapy water revealed bubbles at fittings that looked perfect. Some were poly fittings that should have been brass. Some were connections made when it was too cold — expansion PEX apparently doesn't seal well below a certain temperature, though nobody mentions that in the documentation. Some were fittings that had been cut off and reused after earlier adjustments, leaving tiny score marks on the fitting surface that turned into slow leaks under pressure.
The approach shifted. Heat everything with a heat gun before installation. Replace poly fittings with brass where metal-to-metal contact matters. Cut clean every time — no reusing scored fittings. Re-route sections that were over-complicated or impossible to service. The first section installed on the starboard hull was completely torn out and rebuilt more simply.
By day three, we were writing songs about it. By day five, Shawn switched some of the problem areas to push-to-connect fittings instead of expansion fittings. By day seven, every visible leak was sealed — but the system was still losing pressure with no bubbles anywhere.
🎵 Lying Little Pipe — Here's the song we wrote about our PEX experience.
The decision: park it. Move on. When water is available, pressurize with actual water and see where it goes. At that point, it becomes a wet, messy fix instead of an air leak hunt but hopefully we'll be able to find the water where we can't find the air.
Why It Matters
PEX-A expansion systems are marketed as DIY-friendly. The reality is more complicated. The technique with the expansion tool matters more than the product literature suggests. Temperature affects how well connections seal, and working in an unheated boat in winter creates conditions the system wasn't designed for. Reusing a fitting after cutting it off is nearly impossible without creating a future leak — one score mark is enough.
Poly fittings are not equivalent to brass or stainless in every application. Where a threaded fitting needs to create a solid metal-to-metal seal — particularly under pressure — you simply can't apply enough force to poly to screw it in tight enough. The leaks that persisted longest were almost all poly fittings that should have been brass from the start.
System complexity is a maintenance liability. The first section installed on the starboard hull was functional but over-engineered — too many fittings, crannies, and tight fittings that would be impossible to inspect or service later. Tearing it out and rebuilding it more simply was the right call even though it added a lot of time to the repair.
Stubbornness has limits. At a certain point, continuing to fight the same problem the same way stops being persistence and becomes counterproductive. Switching to push-to-connect fittings for the problem areas wasn't giving up — it was adapting the approach to get the system functional.
Tools / Products Used
PEX-A Expansion System
Electric expansion tool and hundreds of fittings used throughout the fresh water system installation.
Pancake Air Compressor
Rented for pressure testing after the onboard Milwaukee compressor proved insufficient for the job.
Related Episodes
The fresh water pressure tank installation and system design is covered in EP65, where the two large pressure tanks were mounted and the hot water heater connections were completed.
What Comes Next
The fresh water system is installed, and every visible leak is sealed. The system is still losing pressure somewhere, but without water in the lines, there's no way to trace it. That becomes the next problem when water is available — pressurize with actual water and hunt down whatever's left. Until then, it moves to the back burner.
