Getting more hot water from my solar heater - what am I missing?

Yeah, mixing valves are sneaky little things. I’ve seen folks tear apart half their system before realizing the valve was set weird or stuck. Not saying it’s always the culprit, but it’s usually worth a second look - especially after someone else’s been “helpful.” Sometimes I wonder if those things are designed to mess with us on purpose...

Mixing valves really are the pranksters of the plumbing world.

Sometimes I wonder if those things are designed to mess with us on purpose...

I swear mine waits until I’ve got guests over before acting up.

Funny how these things seem to have a sixth sense for timing. I’ve had more than one tenant call in a panic because the “hot water’s gone cold,” only to find the mixing valve was the culprit. In my experience, those valves are both a blessing and a headache - great for safety, but they do seem to gum up or drift out of adjustment at the worst possible moments.

One thing I’ve learned (the hard way) is not to overlook the basics. Sometimes it’s not even the valve itself, but mineral buildup inside it, especially if you’re in a hard water area. A quick clean-out or replacement can make all the difference. I used to think these issues were rare, but honestly, it’s almost routine now.

I’d also double-check your temperature settings. It’s tempting to crank things up when you want more hot water, but there’s a fine line between “nice long shower” and “scald risk.” I always remind myself - and my tenants - that those mixing valves are there for a reason. Had one case where someone bypassed it entirely to get hotter water and ended up with a nasty burn. Not worth it.

If your solar heater’s output seems low, sometimes it’s just the valve restricting flow more than you realize. A small tweak can make a big difference, but I’d always recommend doing it gradually and testing carefully. And if you’re not sure about the valve’s condition, replacing it every few years isn’t overkill. They’re cheap compared to the headaches they cause when they fail.

It’s wild how something that looks so simple can throw off an entire system. Makes you appreciate the old days of just turning on the tap and hoping for the best... though maybe that’s just nostalgia talking.

Mixing valves are sneaky little troublemakers, no doubt. I’ve lost count of how many times I’ve been called out for “no hot water” and it’s just that valve gunked up with scale. Once, I even found a spider nest in one - don’t ask. If you’re still running into issues after cleaning or swapping the valve, check your circulation pump (if you’ve got one). Had a client last winter whose pump was dying and it cut their solar gain in half. Sometimes it’s not the obvious stuff...

Mixing valves really are a pain - had to replace mine twice in the last five years. I totally get the frustration. Sometimes I think folks overlook the pump side of things, like you mentioned. I once spent a weekend chasing a “hot water mystery” only to find out my timer was off by an hour after a power outage... Not always the hardware, but it’s usually something simple (and annoying). Hang in there, you’ll get it sorted.

Ever check if your anti-scald setting is too low? Sometimes those get bumped during repairs or cleaning and limit the hot water. Also, are you sure your mixing valve is rated for solar setups? Some aren’t built for the higher temps.

Also, are you sure your mixing valve is rated for solar setups? Some aren’t built for the higher temps.

That bit about the anti-scald setting getting bumped is spot on. I ran into that at a job last month - customer swore their water heater was “broken” after a plumber swapped out a cartridge. Turned out the anti-scald dial got nudged way down during the install. Easy fix, but it’s not always obvious if you don’t know to look for it.

About the mixing valve, I’ve seen some that just can’t handle the higher temps from solar setups, like you mentioned. Some of the cheaper ones start sticking or leaking when the water gets hotter than what they’re rated for. Did you notice any weird noises or sudden drops in temp at the tap? Sometimes that’s a clue the valve’s not happy.

One thing I’m curious about - do you have a recirc line or is it just a straight run from the tank? Sometimes long pipe runs cool things off before the hot water even gets to you, especially if the pipes aren’t insulated. Just a thought.

I get what you’re saying about the mixing valve, but honestly, I don’t see as many issues with them as folks make out - at least not if you go with a decent brand. Sure, the cheaper ones can stick or leak, but I’ve seen plenty of solar setups running just fine for years with a solid valve. Sometimes I think people swap them out too quick when the real culprit is something else.

Sometimes long pipe runs cool things off before the hot water even gets to you, especially if the pipes aren’t insulated.

That’s a big one in my experience. I’ve lost count of how many “hot water problems” were just cold pipes sucking up all the heat before it ever hit the tap. Even with a recirc line, if your insulation isn’t up to snuff, you’re losing a lot more heat than you think. I’d check your pipe runs and insulation before blaming the valve. Honestly, half the time it’s just heat loss along the way, not the gear itself.

I hear you on insulation making a big difference, but I’ve actually seen mixing valves cause more headaches than folks realize - especially when they’re not sized right for the flow rate. Even with good brands, if the valve’s undersized or not set up for solar temps, you can get lukewarm water or weird fluctuations. Had a job last month where the valve was technically “fine,” but just couldn’t keep up with the demand. Swapped it for a higher-capacity model and the problem vanished. Sometimes it’s not just the cheap ones that act up...

I ran into something similar - thought my solar heater just wasn’t cutting it, but it turned out the mixing valve was the real culprit.

“if the valve’s undersized or not set up for solar temps, you can get lukewarm water or weird fluctuations.”

Mixing valves... the sneaky troublemakers of plumbing. Had a job last month where the homeowner was convinced their solar heater was just “old and tired.” Turned out, the mixing valve was basically bottlenecking all that nice hot water, like a traffic jam but for your shower. Swapped it for one that could handle the higher temps, and suddenly it felt like a spa in there.

Funny thing is, I used to think bigger pipes and tanks were always the answer, but sometimes it’s just that one little valve causing chaos. I do wonder if folks check the temp settings too - seen a few set way low because people are scared of scalding, but then you barely get a warm trickle. Solar setups especially seem picky about the right mix.

Anyway, wild how you can go from ice-cold misery to actual hot showers just by swapping out a part that costs less than dinner out.

“Swapped it for one that could handle the higher temps, and suddenly it felt like a spa in there.”

That’s interesting about the mixing valve. I’ve always assumed if the water was lukewarm, it was either an undersized tank or just not enough sun that week. Never really thought about a single valve making that much difference.

I’m curious - when you swapped out the valve, did you have to mess with any of the anti-scald settings? I’ve read those can be set pretty conservative from the factory, which is safe but not exactly great if you want a hot shower. I’m all for safety, but if I’m paying for solar, I want to actually feel some heat...

Also, does anyone know if certain brands of mixing valves are better for solar setups? Or is it just about making sure it’s rated for higher temps? I’m trying to avoid spending more than I have to, but don’t want to cheap out and end up with the same problem again.

Mixing valves are sneaky little culprits - seen a lot of folks blame the tank or the sun, but it’s often that valve throttling things down. When I swapped one for a solar-rated model, I did have to tweak the anti-scald setting. Factory defaults are usually set for “lukewarm at best,” which is safe but not exactly spa-like. Just don’t crank it too far or you’ll be doing the hot-foot dance.

As for brands, I’ve had decent luck with Watts and Honeywell - main thing is making sure it’s rated for higher temps (some go up to 180°F). Cheap ones tend to stick or get weird with fluctuating temps, so I’d avoid bargain-bin specials if you want consistent hot showers.

Not sure I’d pin it all on the mixing valve, honestly. They can be a pain, but in my experience, solar heaters sometimes just don’t recover fast enough if you’re pulling a lot of hot water back-to-back. Even with a good valve, if your collector or storage tank isn’t sized right for your usage, you’ll still end up with lukewarm showers.

Cheap ones tend to stick or get weird with fluctuating temps, so I’d avoid bargain-bin specials if you want consistent hot showers.

That’s true, but I’ve also seen some higher-end valves act up if there’s mineral buildup - especially in hard water areas. Sometimes folks swap out the valve and still have issues because the lines are gunked up or the check valves are sticking. Worth checking the whole system before dropping cash on a new part.

If you’ve got a recirc loop or booster, those can mask valve problems too. Just saying, it’s not always the valve’s fault.

I’ve run into the same thing with my setup - thought it was the valve at first, but after flushing the lines and cleaning out some scale, things improved a lot. Hard water’s a real pain for these systems. I do wonder, though, how big is your storage tank? I found out the hard way that mine was undersized for our family, especially in winter when the sun’s not as strong. Ended up adding a small electric booster just to get us through cloudy stretches.

Have you checked if your collector is getting enough sun throughout the day? Sometimes shade from trees or even a neighbor’s new fence can sneak up on you and cut down the efficiency. Just curious if you’ve noticed any changes there, or if it’s always been like this.

- Storage tank size is a big one - ran into that myself with a 120L tank for a rental, which just wasn’t enough for a family of four in winter.
- Hard water buildup can really sneak up on you. I’ve started putting in a flush schedule for tenants, but it’s hit or miss if they actually do it.
- Shade’s a silent killer for these systems. Had a neighbor put up a pergola and suddenly my collector output dropped by half - took me weeks to figure out why.
- Electric boosters are a solid backup, but I’d double-check your collector angle and any new shade before investing more. Sometimes just trimming a tree does the trick.

Collector angle really does make a difference, especially in winter. I thought mine was fine until I actually measured it - turns out it was off by about 10 degrees. After tweaking it, I got noticeably more hot water, even without bumping up the booster. Shade’s tricky though; sometimes it’s just a neighbor’s new plant that throws everything off. You’re right about the tank size too - 120L just isn’t enough for a busy household. It’s wild how all these little things add up.

Funny you mention the collector angle - I had the same issue last year. I’d always assumed “close enough” was fine, but after actually checking with a digital angle finder, I realized mine was off by about 7 degrees. It’s wild how much difference a small adjustment can make, especially in the colder months when every bit of sunlight counts.

I’m with you on the tank size too. We’ve got a 150L tank for four people, and even that sometimes feels tight if everyone’s home. I’ve been wondering if insulation on the pipes or the tank itself might help keep the water hotter for longer, especially overnight. Has anyone tried adding extra insulation or maybe even a thermal blanket to their tank? I’m a bit cautious about messing with anything electrical or plumbing-related, but I’ve heard it can make a noticeable difference if done right.

One thing I’m always careful about is making sure nothing’s blocking the collector - leaves, bird droppings, even dust can build up over time. I try to check it every couple of months, but I’m curious if anyone’s found a good way to keep the panels clean without having to climb up there too often.

- I get the temptation to add more insulation, but honestly, I didn’t notice much of a payoff when I tried a thermal blanket on our tank last winter. The pipes were another story - insulating those actually seemed to help, especially the ones running through the garage.
- About panel cleaning, I’ve found that rain does a halfway decent job most months. Unless you’re in a super dusty spot, climbing up there more than twice a year might be overkill.
- For tank size, have you considered shifting showers to spread out hot water demand? We started doing that and it helped more than I expected.

I tried spacing out showers too, but mornings are still a rush at my place. One thing that helped was turning down the flow rate on the showerhead - less water used means the hot lasts longer. Also, I wrapped the pipes last weekend, and it actually made a difference, especially on cold mornings. Maybe not a game-changer, but every bit helps.