Solar water heater overheating and overflowing

[tomkludy]

Hi, I have a 120 gallon solar water heater that was professionally installed several years ago. In the last two years it has developed a problem where it overheats the water and overflows through the pressure valve, creating a river through my garage. I have had the original installer out more than a dozen times to try to fix it and he’s done many different repairs to try to address the problem but with zero success. He even “rebuilt” the tank (whatever that means). He said the only thing left to do is to run a drain line from the pressure valve so that it won’t overflow into my garage. I feel like this is just sweeping the problem under the rug… it should not be overheating in the first place correct?

Is there anything I could do to diagnose and fix the problem myself? As you can imagine I have lost patience with the installer and looking for a diy solution to make this system work like it used to, without overflowing.

I should note that the overheating mostly happens in the summer (Florida is extremely hot and sunny), and I once disconnected power to the rooftop/solar pump, which stopped the overflow. Once I reconnected the pump though, the overflowing started again. Hopefully that helps diagnose what could be wrong.

 

[OzSolar]

Welcome to the forum!

Hi, I have a 120 gallon solar water heater that was professionally installed several years ago. In the last two years it has developed a problem where it overheats the water and overflows through the pressure valve, creating a river through my garage.

Some more details about the system itself would be helpful. Is this a premade product that you can provide a link to?

Just guessing that in Florida that you aren't doing a freeze proof system with anti-freeze.

What's running out? Potable water?

Where's it running out of? A pressure relief valve I assume. On the potable side or the solar loop side?

How about the controller? You might be able to set it shut off at a lower temp. Higher temp = higher pressures so pop-off valves start doing thier jobs but if it's not a drain back system that's not a good idea.

 

[Nobodybusiness]

Hi, I have a 120 gallon solar water heater that was professionally installed several years ago. In the last two years it has developed a problem where it overheats the water and overflows through the pressure valve, creating a river through my garage. I have had the original installer out more than a dozen times to try to fix it and he’s done many different repairs to try to address the problem but with zero success. He even “rebuilt” the tank (whatever that means). He said the only thing left to do is to run a drain line from the pressure valve so that it won’t overflow into my garage. I feel like this is just sweeping the problem under the rug… it should not be overheating in the first place correct?

Is there anything I could do to diagnose and fix the problem myself? As you can imagine I have lost patience with the installer and looking for a diy solution to make this system work like it used to, without overflowing.

I should note that the overheating mostly happens in the summer (Florida is extremely hot and sunny), and I once disconnected power to the rooftop/solar pump, which stopped the overflow. Once I reconnected the pump though, the overflowing started again. Hopefully that helps diagnose what could be wrong.

Have you ever tried just replacing the Pressure Release valve? Sometimes they go bad.

Worth a shot and inexpensive.

 

[Philip53]

Pictures and details of your system would be most helpful. There are many types of solar hot water systems. I installed a drainback system 13 years ago, with an 80 gallon SS tank with electric backup. I found out real quick that the two 3 x 10 roof mounted solar collectors could bring the water up to over 160 degrees. I turned it down as low as the pump/controller would allow, and I used a tempering valve, but still the domestic hot water side was really hot. This increased the pressure as the water expanded. I added an expansion tank, and that elimated the excess pressure. The water pressure could be exceeding the rating of your pressure valve, allowing it to blow off or leak from the additional pressure. You should have had guages installed where you could monitor incoming water pressure as well as the heated hot water pressure exiting your tank.

I don't know if your system is experiencing this issue, but I would look at this.

 

[RCinFLA]

Is the system self-circulating with tank higher than panel or do you have a small circulating pump?

You may have a restriction in the water line or defective/clogged pump that is reducing water flow.

Panel produces so many btu's of heat from sun's illumination. The less the amount water pushed through, the hotter that smaller amount of water will be. The water may boil if flow rate is very low. Water does expand in volume a little at higher temps but it is not that much unless phase changed to steam gas pressure from high amount heating.

The tank temperature keeps rising during the day if not enough hot water is being used. Has there been a change is usage rate in the last two years, like less people living in house.

The heat may have degraded the pressure relief valve. Check the water pressure.

You should at least have a readout on fluid temp leaving solar panel.

 

[rogerheflin]

If you fill the system full with cold water and then heat it, then the pressure will go up and water will leak out, and the water does not need to get abnormally hot. On a normal hot water tank the solution is an expansion tank to let the water expand when it is heated.

I knew a co-worker that had his new tank leaking out like this and to confirm the relief valve was working right I loaned him a pressure gauge. He observed that when the tank heated the water up the pressure on the gauge (max 120psi) just kept going up above 120psi until the release valve released some water. the plumber came back and added an expansion tank.

If you have an expansion tank then that expansion tank may no longer be working/pressurized.

The expansion tanks are sized based on the number of gallons in the hot water system.

 

[1234enough]

If your system is a sealed system without an expansion tank, I'd be seriously worried- see link

.

More details required- what heats the water? Solar thermal- closed system / drain back system, PV electricity? Ect ect.

 

[tomkludy]

Thanks for the responses, I have been busy but will try to answer all...

Some more details about the system itself would be helpful. Is this a premade product that you can provide a link to?

This is the system: https://www.americanwaterheater.com/media/20993/ncess00708.pdf

It has two thermostats, one for the solar side and one for the resistive heater side.

What's running out? Potable water? Where's it running out of? A pressure relief valve I assume. On the potable side or the solar loop side?

It is coming out from the pressure valve directly on top of the tank. This one:

How about the controller? You might be able to set it shut off at a lower temp. Higher temp = higher pressures so pop-off valves start doing thier jobs but if it's not a drain back system that's not a good idea.

By controller, are you referring to this?


This red thing has lights that come on when the solar pump is running. You can see it is connected to power, which I believe is connected up to the small PV solar panel that powers the pump. If those wires are disconnected, then the tank stops overflowing, but it also stops heating with solar and falls back to only using the resistive heater.

Have you ever tried just replacing the Pressure Release valve? Sometimes they go bad.

Yes, the installer has replaced the pressure release valve every time they came to do service, probably a dozen times.

 

[tomkludy]

Is the system self-circulating with tank higher than panel or do you have a small circulating pump?

I am pretty sure that there is a pump, powered by a small solar PV panel. See above - the red device on top. If this is disconnected then it stops overflowing but also stops using solar for heating (according to the installer).

You may have a restriction in the water line or defective/clogged pump that is reducing water flow.

How would I check this?

Has there been a change is usage rate in the last two years, like less people living in house.

No change in the number of people. If anything my kids have been taking longer showers, but always in the evening.

The heat may have degraded the pressure relief valve. Check the water pressure.

You should at least have a readout on fluid temp leaving solar panel.

There are no displays or readouts on this system, at least not that I am aware of.

If you have an expansion tank then that expansion tank may no longer be working/pressurized.

The expansion tanks are sized based on the number of gallons in the hot water system.

We do have an expansion tank, here's a picture of it:

It's model "Backstop 12-A102". This seems like a promising thread to investigate though. Looking at the tank sizing guide (https://backstop.net/tank-sizing-guide/) it seems like with a 120 gallon tank this should be OK up to ~82psi supply pressure. I have no idea what my supply pressure is. I also do not know how to tell if this expansion tank is working as expected. Any way to test this?

 

[1234enough]

https://www.americanwaterheater.com/media/20993/ncess00708.pdf is a link to the thermal storage tank, this only makes up one part of the system.

Without knowing the whole system it is difficult to determine any issues.

For instance if the system has closed loop solar thermal and doesn't have any form of heat dump it will overheat the system if no hot water is taken from the storage tank.
If the sun heats up the collector and the heat has no where to go, it will either overheat the tank or the collector system and this will be in the form of boiling liquid.

As system has an expansion vessel- is this correctly pre pressurised? - this won't help if the above is happening.

 

[Solar Guppy]

Your system should have a pressure releif valve at the high point in the system, which should be on the outlet on the panel on the roof. The pressure relief on the HW tank is a last resort and if that is releasing, the one on the roof is either not installed or not functional.

Not running the circulator can lead to complete failure of the collector on the roof as it will make stream that will crack joints. When I sold the home I installed the solar hot water system on the lady one day unplugged the controller and then had water pouring into the garage as the pipe burst.

In the end, I found the system problematic and not worth the effort and a few extra PV panels offset any usage a traditional hot water tank uses in energy and would never install one again.

 

[OzSolar]

I am pretty sure that there is a pump, powered by a small solar PV panel. See above - the red device on top. If this is disconnected then it stops overflowing but also stops using solar for heating (according to the installer).


How would I check this?


No change in the number of people. If anything my kids have been taking longer showers, but always in the evening.


There are no displays or readouts on this system, at least not that I am aware of.


We do have an expansion tank, here's a picture of it:
View attachment 269148
It's model "Backstop 12-A102". This seems like a promising thread to investigate though. Looking at the tank sizing guide (https://backstop.net/tank-sizing-guide/) it seems like with a 120 gallon tank this should be OK up to ~82psi supply pressure. I have no idea what my supply pressure is. I also do not know how to tell if this expansion tank is working as expected. Any way to test this?

I bet this has been your problem the entire time. Pressure tank is probably good but your city pressure is already so high that's no room left for it to expand and contract to absorb the difference in pressure as the day goes on.

Compare it to the shock absorber bottoming out on an already overloaded pickup truck when you hit a pothole.

If you didn't have a back flow preventer between you and the city this would not happen but of course that's required by code.

I see a few options after you confirm the pressure tank is good. You can google the instructions for checking the pressure tank. A quick test is too remove up the valve stem cap (like a car tire) and see if water comes out. That means the bladder is bad.

-Reduce the pressure to your house which will involve a "pressure reducing valve" but that stinks because you probably like your nice city pressure.

-Add a larger or 2nd pressure tank

 

[Q-Dog]

The expansion tank could be waterlogged. Is should be mostly air in that tank. Can you knock on it and tell if it sounds hollow or full of water?

 

[rogerheflin]

I am pretty sure that there is a pump, powered by a small solar PV panel. See above - the red device on top. If this is disconnected then it stops overflowing but also stops using solar for heating (according to the installer).


How would I check this?


No change in the number of people. If anything my kids have been taking longer showers, but always in the evening.


There are no displays or readouts on this system, at least not that I am aware of.


We do have an expansion tank, here's a picture of it:
View attachment 269148
It's model "Backstop 12-A102". This seems like a promising thread to investigate though. Looking at the tank sizing guide (https://backstop.net/tank-sizing-guide/) it seems like with a 120 gallon tank this should be OK up to ~82psi supply pressure. I have no idea what my supply pressure is. I also do not know how to tell if this expansion tank is working as expected. Any way to test this?

If that pressure valve is leaking only when it is heating water then the expansion tank must not be working right. If the water main system pressure was too high then it would be leaking off and on all of the time even when not heating. I know my reverse osmosis pressure tank (very similar design idea) stopped working that i had to use an air compressor to get air back into it above the bladder so it would start working (have capacity to supply a gallon or 2) again. You might be able to feel and/or tap on the sides of the expansion tank and determine how high up the water level is in it.

 

[RCinFLA]

Typically the expansion tank is precharged to about 50 psig. There should be an air valve like a tire stem on top to charge it.

Some water utilities require check valves to prevent reverse water flow into the water mains. It may be incorporated in utility's water meter. When there is a utility check valve you need the expansion tank to take the system volume bloating from heat expansion within your house water lines.

Water solar panels can increase the volume of water that is exposed to heat expansion so an expansion tank for a normal non-solar water equipped house may not provide enough expansion cushion.

 

[Spacecadetdave]

Hi, I have a 120 gallon solar water heater that was professionally installed several years ago. In the last two years it has developed a problem where it overheats the water and overflows through the pressure valve, creating a river through my garage. I have had the original installer out more than a dozen times to try to fix it and he’s done many different repairs to try to address the problem but with zero success. He even “rebuilt” the tank (whatever that means). He said the only thing left to do is to run a drain line from the pressure valve so that it won’t overflow into my garage. I feel like this is just sweeping the problem under the rug… it should not be overheating in the first place correct?

Is there anything I could do to diagnose and fix the problem myself? As you can imagine I have lost patience with the installer and looking for a diy solution to make this system work like it used to, without overflowing.

I should note that the overheating mostly happens in the summer (Florida is extremely hot and sunny), and I once disconnected power to the rooftop/solar pump, which stopped the overflow. Once I reconnected the pump though, the overflowing started again. Hopefully that helps diagnose what could be wrong.

I have the same problem. I purchased this house here in Florida with a 80 gal solar water heater. Maybe 5 years old at the most. Apparently the company that installed the unit is out of business. A common thing around here with companies getting the money and running. I have had a professional company replaced the plumbing and serviced the system. Still have overflow and excessive calcium buildup. I have valves which I shut off the solar part and now just have a regular water heater. Im trying to fix it myself. Any suggestions would greatly be appreciated.

 

[Philip53]

Is your leak also at the T&P valve? Unless it is a bad valve, or has something stuck under the seat, it is experiencing too high a temp or too much pressure - either is bad. An expansion tank, an additional one, or a larger one may help also. A decent plumber should be able to figure this out very quickly. My solar system is an indirect drainback system, using a controller to decide when to pump water up to the solar collectors. Indirect means that the heated water flows through coils inside my SS tank, heating the domestic hot water.

 

[400bird]

So, I've got a question for the experts in these types of solar water heating (which I am not)

Here's my understanding of a couple of basic facts on these systems:
You need to continually have water flowing through the panels to keep from boiling water, creating steam, which corrodes/eats the solder joints and causes massive pressure increases.
I think this means that there's no way to limit/control water temperature in the tank. An expansion tank may help with the pressure, but the temp could still be dangerously hot.

Would installing something to dump the heat help keep the water temp (and to a lesser extent pressure) down?
I don't know the approximate kW rating of these panels to size the heat dumping radiator, but I'm thinking something similar to a car heater core with fan. But that may not be large enough to dump enough heat. Might need a full size radiator, or equivalent.

 

[Philip53]

A heat dump loop can be used on a closed loop solar hot water system to reduce pressure & temps. Using a closed loop system in Florida without a method to reduce temperature and thus pressure seems a bit strange. As @400bird mentioned above, the system can increase temps and pressure significantly without a pressure relief valve or a way to dump the excess heat. A controller opening a diverter valve to a dump loop, or some other heat dissipating apparatus would work. Failing this, the only thing that can happen is the emergency T&P valve opening under the excess heat/pressure. It is just doing its job, but this means to me that the entire system is operating on the edge, and could prove dangerous should a component(s) fail.

 

[OzSolar]

I think this means that there's no way to limit/control water temperature in the tank. An expansion tank may help with the pressure, but the temp could still be dangerously hot.

Batch heaters for non freezing's climates are great.

For climates that rarely freeze then an open loop system with freeze sensors is a good choice. It pumps water that you've already heated into the panel to prevent it from freezing and breaking. Sounds like terrible idea but for once or twice a year it's fine and the system much simper = cheaper and more reliable. However these systems are not immune to power outages. No pumping means bad things happen.

If you have to have a freeze proof system then "Drainback" systems solve pretty much every issue with solar hot water heaters. Tank meets the set temp, pump shuts off and the liquid in the solar panel drains back into the drain back tank which lives in your cozy mechanical room. These systems ARE immune to power outages because every failure mode results in the pump stopping and the collector draining out.

Has anyone mentioned that the OP's expansion tank is probably bad so as the day goes on and the system heats up the pressure has increased to the point where the T&P valve activates? If not then someone probably should mention that. (sorry I couldn't help myself)

 

[sumpower]

In the end, I found the system problematic and not worth the effort and a few extra PV panels offset any usage a traditional hot water tank uses in energy and would never install one again.

Same result here. Now all my hot water is provided by extra (cheaper) solar panels. No maintenance required so far.