Hey everyone! I have a 200L low pressure solar water heater up on my roof that comes with a small header tank. Lately, I've been noticing that on cloudy days, the heater struggles to warm up the water. If someone takes a shower, cold water comes in to fill it back up, which drops the overall temperature of the water! I'm considering installing a smart valve on the cold water inlet to limit refills to the mornings only, so the tank retains the heat it gets throughout the day. But I'm curious—does the tank need to stay full for any safety reasons? I see there's a bleed tube at the top, so I'm not worried about pressure build-up, but I want to make sure I'm not overlooking any potential issues. After all, a lower pressure hot shower sounds way better than a cold one!
3 Answers
That's an interesting idea! But just to clarify, if you're not trying to fill it with anything other than water, I think you'll be fine. Just make sure air can vent through the bleed tube as the water level changes. A bit of careful design should keep things safe!
I had a couple of those systems, and what I did was add a submersible heating element with a thermostat. It set it to around 94-100°F, and it didn’t kick on much on cloudy days. It was super efficient, and I didn't see much change in my electricity bill—maybe that's an option for you?
That’s cool, but I’m off-grid and already struggling with energy use on cloudy days. Diverting power to heat water is tough when you need it for other things!
For the most part, yes, keeping the tank full is important to avoid potential damage and keep it working efficiently. It's worth ensuring that it doesn’t drop too low. Just my two cents!

Yeah, air will definitely get in through the bleed. Just make sure that mechanism is working as expected!