Tankless water heaters: casing leaks versus connection leaks

Funny you mention the knees - I swear mine creak louder than the cabinet doors these days. I’ve always wondered, do you think those slow leaks at the valve are more likely to go unnoticed than a trap leak? I feel like the connections are sneakier, but maybe I’m just paranoid after finding a puddle under my kitchen sink that turned out to be from a loose supply line. Ever tried those colored leak detection tablets, or do you just stick with the flashlight routine?

I get what you mean about the sneaky leaks at the valve, but honestly, I’ve had more trouble with trap leaks over the years. Maybe it’s just my luck, but when a trap goes, it tends to drip right onto the bottom of the cabinet and you don’t notice until there’s a musty smell or the wood starts swelling. Valves, at least in my experience, usually leave a telltale mineral stain or crust if they’re leaking slow.

I’ve never bothered with those colored tablets - seems like overkill unless you’re dealing with a toilet or something you can’t see behind. I just run my finger along the connections and check for moisture every couple months. Flashlight helps, but sometimes it’s just about getting your hand in there and feeling around. Found a slow drip that way last winter, saved myself a bigger headache down the line.

Drips from a trap are sneaky, I’ll give you that. The worst ones seem to happen right where the plastic meets metal - those cheap slip joints with the thin washers almost always loosen up over time, especially if folks are tossing stuff under the sink and jostling things around. Had a call last year where someone lost half their cleaning supplies to a slow trap leak before they even noticed. The bottom of their cabinet was basically compost by the time I got there.

But I still think valve leaks are underestimated. Sure, you might get a mineral crust or a little green stain, but I’ve seen more than one “just a crusty valve” turn into a full-blown spray when someone tries to shut it off in an emergency. Those old multi-turn valves are notorious for failing right when you need them most.

I’m with you on the tablets though - never saw much point unless you’re testing for something behind a wall or in a spot you can’t reach. A good old flashlight and your hand will catch 90% of problems early, if you remember to look.

Those crusty valves are a nightmare, I agree. Had one snap off in my hand once - water everywhere, tenant freaking out.

“Those old multi-turn valves are notorious for failing right when you need them most.”

- Had a similar situation with a multi-turn valve - tried to shut it off, and the stem just spun. Ended up with a slow leak that turned into a full-on drip overnight. Not fun.

- Swapped a few out for quarter-turns, but I’m not totally sold yet.
- They’re definitely smoother and easier for everyone to use.
- But I’ve had one start seeping at the packing nut after about two years. Not catastrophic, but still annoying.

- From what I’ve seen, leaks at the connection points are usually worse than a drip from the box itself. Connections can spray or flood if they go bad, while a box drip is more of a slow creep (unless you ignore it).

- I do wonder about the environmental impact of tossing all those old valves though... seems wasteful, but maybe it’s worth it for peace of mind.

- Anyone else notice quarter-turns sometimes get stiff if they’re not used for a while? Or is that just cheap brands?

Honestly, neither option feels perfect, but at least quarter-turns don’t crumble in your hand when you need them most.

Had a quarter-turn seize up on me after maybe three years - barely used, too. Had to put some real muscle into it, which kind of defeats the point. Multi-turns have failed on me as well, but at least you usually get a warning before they totally give out. I agree, leaks at the connections are way more stressful. A slow drip is annoying, but a blown fitting can ruin your day fast. Still not sure there’s a “best” option... just less bad ones.

Quarter-turns seizing up is more common than people think, especially if they sit unused for a while. I’ve seen multi-turns start to weep for weeks before they finally go, which at least gives you some warning. You’re right, a blown fitting is a nightmare - damage adds up fast. Honestly, there’s no perfect valve, just regular checks and a bit of luck sometimes.

Honestly, there’s no perfect valve, just regular checks and a bit of luck sometimes.

That’s the truth. If I had to pick, leaks at the connections are worse, hands down. Drips from the box are usually slow and give you a fighting chance to catch them before they do real damage. A connection leak, especially under pressure, can go from nothing to a full-on flood in minutes. Seen it happen more than once - one time a supply line nut let go behind a washing machine and the homeowner was out for the afternoon... carpet, drywall, even some electrical got trashed.

Quarter-turns seizing up is a pain but I’ve had more callbacks from compression fittings working loose or threads not sealing right. Regular checks help but honestly, most folks don’t look until there’s water on the floor. If you’re worried about either, shutoffs and braided hoses are cheap insurance compared to fixing water damage.

I hear you on the compression fittings - those things always make me nervous, especially if I’ve had to move the machine for cleaning or whatever. But here’s a question: do you trust those braided hoses over the standard rubber ones? I swapped mine out last year and felt like I was buying peace of mind, but sometimes I wonder if I’m just falling for marketing hype. Either way, replacing drywall is way more expensive than a new hose... learned that the hard way after a slow leak wrecked my laundry room baseboards.

But here’s a question: do you trust those braided hoses over the standard rubber ones?

I get the peace of mind angle, but honestly, braided hoses aren’t a total cure-all. They’re definitely better than plain rubber, but I’ve seen plenty of failures - usually at the crimped ends where the metal meets the hose. That’s where slow leaks sneak up on you. Like you said, “replacing drywall is way more expensive than a new hose,” but I’d add: regular inspections are just as important as what type of hose you use. Even the best hoses can go bad if they’re out of sight and out of mind for too long.

I hear you - those crimped ends are the real weak spot. Seen one start dripping behind my washer and it was a mess. I swap mine every five years, no matter what. Braided’s better, but not invincible. Out of sight, out of mind gets expensive fast.

Honestly, you nailed it - those crimped ends are sneaky. I’ve seen a “just a drip” turn into a full-on puddle under the laundry room floor. Swapping every five years is smart, even if it feels overkill. I do think sometimes people trust braided lines too much, though. They’re better, but like you said, not bulletproof. Out of sight really does mean out of mind... until you’re mopping up at midnight. Good call staying ahead of it.

I get the logic behind swapping every five years, but honestly, I’ve seen some lines last a decade without issues - especially if you’re using quality parts and not over-tightening connections. Sometimes, leaks at the box itself are overlooked, and that’s where the real mess starts. Connections are easier to spot and fix, but a slow drip from the valve or box can rot out a wall before you even notice. I’d argue those hidden box leaks are worse in the long run.

Sometimes, leaks at the box itself are overlooked, and that’s where the real mess starts. Connections are easier to spot and fix, but a slow drip from the valve or box can rot out a wall before you even notice.

That’s a really good point about hidden box leaks. I’ve always been more worried about those than anything at the joints or connections. I mean, if you’re checking under your sink every now and then, you’ll probably catch a loose fitting or a bit of seepage around a hose pretty quick. But that slow drip inside the wall? That’s nightmare fuel for anyone on a budget.

I get what you’re saying about lines lasting ten years or more if you use decent parts and don’t crank things down too hard. I’m in the same boat - replacing stuff every five years just because seems wasteful if everything looks solid. But then again, it only takes one sneaky leak to ruin your day (and your drywall). I had a shutoff valve behind my washing machine that dripped so slowly it took months to notice... by then, there was mold creeping up behind the baseboard. Not fun.

Still, I do wonder if there’s a middle ground here. Maybe instead of swapping everything on a schedule, it makes sense to do regular checks - like actually pulling out appliances or opening up access panels once in a while? It’s not always convenient, but it beats tearing out soggy drywall later.

Anyway, thanks for bringing up the “hidden” factor with box leaks. It’s easy to focus on what we can see and forget about what’s going on behind the scenes (or walls). Makes me want to double-check those spots I usually ignore...

Ever tried those little leak detectors you can stick behind appliances or under sinks? I’ve thought about getting a couple, but not sure if they’re worth it or just another gadget to forget about. Anyone actually caught a hidden drip with one?

Ever tried those little leak detectors you can stick behind appliances or under sinks? I’ve thought about getting a couple, but not sure if they’re worth it or just another gadget to forget about.

Honestly, those detectors have saved a few of my clients from nasty surprises. They’re not perfect, but catching a slow drip early beats finding out after the cabinet’s warped. Worth it for peace of mind, especially under old sinks.

Had a call last winter - guy had a slow drip behind his dishwasher, went unnoticed for weeks. By the time he smelled the musty odor, the floor was buckled. Those little detectors would've beeped on day one. They're not fancy, but they do their job. I always say, a $20 sensor beats a $2,000 floor repair. Just remember to check the batteries every now and then... learned that the hard way myself.

Leaks at the connections are usually easier to spot, but those sneaky drips from the box? They’re the real wallet killers. Had a customer once who thought it was just “humidity” under his sink... turned out to be a slow leak that rotted half his cabinet. Sensors are cheap insurance, honestly.

Had a rental where the “just a drip” from the box quietly soaked into the particleboard for months. By the time anyone noticed, the whole bottom shelf was mush. Ever tried to explain that to a tenant? Curious - anyone here ever had insurance actually cover that kind of slow damage, or is it always considered “maintenance”?

Drips are sneaky, I’ll give them that. Had a similar thing happen under my kitchen sink - just a tiny drip from the shutoff valve, but it turned the cabinet base into oatmeal over a few months. The worst part? My insurance guy gave me the “maintenance issue” speech. Apparently, unless it’s a sudden burst or something dramatic, slow leaks are usually on us.

Curious - anyone here ever had insurance actually cover that kind of slow damage, or is it always considered “maintenance”?

From what I’ve seen (and read on way too many forums), insurers almost always call it “wear and tear.” If you can prove it was sudden, maybe you’ve got a shot, but good luck convincing them. Honestly, I’d take a connection leak over a slow box drip any day... at least you notice those before your shelf turns into pulp.