Solar Hot Water Dumping Dangerous Scalding Water onto patio

techdiver

Hi,

I have a question regarding my Solar hot water system. It came with the house when we bought it and the overflow pipe was dumbly positioned over our patio. Now we seem to have an issue on long sunny days that eventually a massive amount of scalding water will start dumping from this overflow pipe on top of anyone outside. It's not a drip it's a full on dump.

All our neighbours have the same system without the same issue. I understand the concept that if the water gets too hot it needs to relieve pressure but what I don't understand it why this basically dumps all the water until it empties the tank of hot water completely? I would have assumed it just needs to dump excess and stop but it goes for minutes dumping scalding water onto my patio from a height.

Has anyone any ideas what is happening here? The only way I mitigate it is to keep an eye on the tank temp by looking in my hot-press and running the bath every now and then, but surely the system isn't as dumb as that?

John.G

If you have a pressurized system then this should not happen as the expansion vessel should hold the contents of the evacuated tubes or the flat plates, it has a pressure relief valve set to 6bar, if this lifts repeatedly then it should stop releasing solar fluid once ~ 8/10 litres have been expelled. The system then has to be recharged with solar fluid after ensuring the E.vessel is precharged with air to 1.5bar or so. Evacuated tube systems should ideally have a dump radiator to take excess heat, I have flat plates and very soft water so I have the store/cylinder temp set to 85C as the plates will never rise higher than ~ 80c, I also have a antiscald valve on the cylinder outlet to reduce the temperature to 55C/60C.

Markcheese

Also a pipe should be bringing the hot water down to ground level , so it doesnt scald anyone ..

Markcheese

Short term ,Could you draw off a bowl or 2 of hot water on sunny afternoons ..

dathi

https://www.boards.ie/discussion/comment/120719085#Comment_120719085

sounds more like he has a pressurised cylinder and it is the pressure relief valve on the cylinder that is opening this would suggest that either the pressure vessel has failed and needs ether to be re charged on air side or replaced , or the pressure relief valve is faulty , or he has not set a limit on the temperature that the cylinder can reach before either shutting off or heat dumping into a radiator , the over flow pipe should have been routed to a drain

John.G

That makes sense, if its a unvented cylinder then the T@PRV will open when the cylinder temperature reaches 95C., a rather novel heat dump!!!

techdiver

https://www.boards.ie/discussion/comment/120719110#Comment_120719110

That's what I have been doing, but sometimes forget. If I do and this process starts it essentially dumps water for 10-15 minutes without stopping.

John.G

At least you can get that piped away to a drain but if you have a vented HW cylinder with a feed and expansion tank then this can be downright dangerous if the tank isn't metal (which it should be with a solar coil in the cylinder), the tank (cistern), if plastic, can fail due to the scalding hot water and not only water damage your house but possible injure someone directly below when it comes through the ceiling.

dathi

https://www.boards.ie/discussion/comment/120721151#Comment_120721151

put up some photos of your cylinder and the solar controller box