Problem with solar hot water losing pressure.

[sprint72]

Hi all

I have a older sunstream hot water solar system. Never touched it for 20 years and I think it worked. The roof started leaking under the panels and that's when the fun started. Fixed the roof and put panels beck in place. I used sierra anti freeze which is a automotive propylene glycol to fill the system. The problem is it will hold the pressure for a couple of days everything works and then I check and I lose the system pressure. It goes down to like 10lbs. This has happened a couple of times already. Could not find any visible leaks on the roof until I cleaned the gutters and the water in there was green. Still cannot find a visible leak in the panels.

Now I drained the system and filled with water to 25lbs, and when pump is on pressure is about 35lbs. This has been working for 2 days now. I am now waiting for it to lose it's pressure again, only this time I will only lose water and much easier to fill with water.

I replaced the expansion tank, and the pressure relief valve last year when I fixed the roof. Does anyone have any idea what is happening?

Thanks
Tom

[inetdog]

Now I drained the system and filled with water to 25lbs, and when pump is on pressure is about 35lbs. This has been working for 2 days now. I am now waiting for it to lose it's pressure again, only this time I will only lose water and much easier to fill with water.

I replaced the expansion tank, and the pressure relief valve last year when I fixed the roof. Does anyone have any idea what is happening?

Thanks
Tom

1. Check whether it is the pressure relief valve (if it is mounted outside) by wrapping with cloth or looking for green drip trails.
2. Possibly you have a solder joint which is holding pressure at low temperatures but is leaking when temperature cycled. Can you tell whether the leak is happening while the pump is on or while it is off?
3. Pressurizing to more than 35 PSI (but still within the limits of the plumbing) may show the leak immediately.

[peakbagger]

It does sound like a marginal solder joint. Alternatively your expansion tank could be waterlogged. If tank is waterlogged, the pressure will rise substantially when the panels are heated and it will find a way out, usually via the pressure relief valve. Of course when the panel cools down it will then usck a bit of air in.

[sprint72]

It is still holding pressure and making hot water since Wednesday. Also very hot here in NJ over 90 degrees the last 5 days. Pressure is 25 with pump off and 35 when pump is running. Does the antifreeze heat up more than water does?
Also is the Sierra anti freeze OK to use?

I am thinking just use water and drain for the winter since it doesn't make a lot of hot water during the winter anyway. I will see how long it runs before losing pressure again, hopefully it does not.

[peakbagger]

Sierra appears to be propylene glycol so it will work. Some argue the additive package is different for auto than panels but i wouldn't worry about it. There could be some crud loosened up as the original system was most likely ethylene glycol. Some folks recommend running a coil cleaner that HVAC folks use though the system on occasion to clean out any deposits. D invest in some pH test strips and check the pH of the glycol every year or so, if you overheat it by stagnating the panels, it can go acidic and that can lead to panel leaks.

I run my panels year round in a colder climate, I have a DC pump and at some point when its subzero the glycol gets thick enough that my pump will not pump it but most of the time I use it to preheat my incoming hot water to my winter time hot water source which is a insulated tank heated by a zone on my oil or wood boiler. I need to switch a couple of valves in the spring and fall. The DC pump doesnt cost anything to run since it on a solar panel, but maybe there is slight savings in not running an AC pump.

[sprint72]

Lost pressure again yesterday, I checked in the morning and it was fine, when I check last night it was at 12lbs. Yesterday was not as hot or sunny as the previous couple of days. I know there is a leak somewhere but it was holding at 35lbs.

The 80 gallon hot water tank was hot so maybe after a couple of days the heat exchanger is not cooling the panels enough, don't know. The pressure relief is in the basement and that is holding, is the pressure higher up at the panels?

It is easy to fill now that I am just using water.

[peakbagger]

The pressure is the same no matter where you measure it in a presurized loop.

Could you sketch out the system? I am interested if you have an expansion tank in the loop.

[sprint72]

I will take a picture of it tonight.

[sprint72]

solar.jpg

[peakbagger]

The expansion tank orientation is a potential issue. Normally they are mounted with the connector on the bottom vertically, if the bladder fails there is still some reserve capacity. If you unscrew it and it sloshes after you have drained it, the bladder has a leak into the air chamber. To check it fill it up with water and pour it out into a bucket, the normal liquid volume should be half the tank volume.

I am getting concerned that you havent found a leak point. it definitely sounds like you have an intermittent leak, with the bladder functioning at the proper charge pressure, the pressure in the system with the pump off shouldnt change appreciably from no sun to full sun as the bladder absorbs the volume change, if the pressure does change with the pump off, the bladder is either full or has lost its precharge. . About all you can do is roam around with some leak tech and soap all the joints.

[inetdog]

About all you can do is roam around with some leak tech and soap all the joints.

Pressurizing the system temporarily with air will make finding the leak a lot easier in two ways:
1. Air bubbles are a lot easier to see than liquid drips.
2. Air will leak noticeably through a bad joint that will only fail and leak water when at a higher pressure or temperature.

[sprint72]

Yesterday morning I refilled the system and it lost it's pressure pretty quick. I filled to 20lbs and within a 1/2 hour it was down to 14 and this morning almost down to 10. I did not have time to go on the roof to look for leaks. Hopefully Saturday I can refill and I find a leak. Peak bagger thanks for your help.

[peakbagger]

Not sure you picked up on prior post, but inetdog filled in something I skipped. Drain the system and pressurize it with air, then go around with soapy water and check all joints. Air leaks will be easier to find then water leaks.

By the way if you are up on the roof make sure you have fall protection or some way of stopping you from falling off the roof. Easy to take a misstep when you are concentrating on something else.

[sprint72]

I missed inetdog post also, hopefully Saturday I can get on the roof and check for leaks, just have to come up with something to hook up the air hose to the system. I have a compressor so that is not a problem. I guess I will try to shoot for 35lbs of air pressure and go from there.

Thanks inetdog.

[sprint72]

I pressurized the system to 25lbs with air. Went on the roof and found the leak right away. It was a union that was loose. I tightened it up and refilled with water. Yesterday it made 80 gallons of hot water. Hopefully pressue will hold and I can refill with the antifreeze. Thanks again for your help.

Tom