Could Solar System Blow Up?

Public2015

Sorry if this is a stupid question. I don't know enough to make a call on this..I have a Velux domestic solar hot water system that heats my water tank. There is a control panel next to the hot water tank. In today's heat, the Velux digital display showed the collector (ie the solar panels) at 140C, the bottom of the tank at 58C and the top of the tank at 58C. There was also a digital exclamation mark in a circle and it sounded like there was no water moving through the system.

My plumber, who installed the system, installed a separate small water pump on a timer to push hot water down to one bathroom radiator which he said was a heat dump for days when the sun was hot and the solar system was getting very hot.

So, I turned on the small heat dump pump and the Velux digital display showed the temperature at the panels coming down slowly (to 100C) and the bottom and top of the tank going up to 61C each. There are also two non-digital temperature gauges next to the control panel, one surrounded by blue plastic and one by red plastic. The needle on the red gauge started rocketing up from about 80C to over 120C at a fast rate - it maxes out at 120C. The rate at which it was going up looked bad, so I turned the heat dump pump off again.

The system has now settled at the collector at 100C and the water tank at 61C. The red gauge has gone back down to 80C. The blue gauge is at 65C - it didn't move. There is also a pressure gauge - it is at 3.5 bar. The exclamation mark is still there on the digital display and there is no water moving through the system.

My question is this. Is the Velux system designed to shut itself down as a safety measure when the water gets too hot? Am I potentially creating a problem by having the separate heat dump pump on a separate timer pushing water through the system - should I just switch that pump to "constant off" and let the Velux system control itself?

The hot water tank is also connected to a solid fuel stove, an electric immersion and OFCH as well.

Thanks - worried the whole thing could blow if I do the wrong thing now that we have some sunshine and summer heat.

freddyuk

When you switched on the by pass pump the hot water started to move through the system again thus the tank gets hotter and the collector gets cooler. It sounds like your bypass is just a loop within the existing system thus it still heats the cylinder! What you need is a diverter valve that diverts ALL the flow into the radiator circuit when it is too hot. The radiator is sized to lose the amount of heat created by the collector. Most decent controllers have a bypass function already loaded they just need a plumber to install the pipework correctly. It should not be a manual switch as what happens if you are on holiday??!!
If you just let the system do it's own thing then your glycol will turn to tar and you will need expensive repairs to sort it out as the pump, valves and expansion tank can all get damaged unless the temperature is properly controlled.
It will not blow up but it will potentially send hot fluid out of the safety valve.
Post some images of the pipework to confirm if you need to replumb......

Public2015

freddyuk wrote: »

When you switched on the by pass pump the hot water started to move through the system again thus the tank gets hotter and the collector gets cooler. It sounds like your bypass is just a loop within the existing system thus it still heats the cylinder! What you need is a diverter valve that diverts ALL the flow into the radiator circuit when it is too hot. The radiator is sized to lose the amount of heat created by the collector.

Yes, that is what is happening. But the only radiator which gets hot is the one small towel rail in the bathroom which is acting as the heat dump. The pipe work beside the water tank and the bypass pump itself get hotter than hell though.

Most decent controllers have a bypass function already loaded they just need a plumber to install the pipework correctly. It should not be a manual switch as what happens if you are on holiday??!!

There is a standard analogue timer attached to the bypass pump.. It is normally set to come one for two hours every day automatically from 1pm to 3pm. It can also be switched to constant off and constant on.

If you just let the system do it's own thing then your glycol will turn to tar and you will need expensive repairs to sort it out as the pump, valves and expansion tank can all get damaged unless the temperature is properly controlled. It will not blow up but it will potentially send hot fluid out of the safety valve.
Post some images of the pipework to confirm if you need to replumb......

I'll take some photos later on thanks. My main question though is whether the main Velux control unit is set up to manage all of this automatically or should I continue to leave the bypass pump on timer. Presumably every solar system can over heat in summer, so should this not be a normal function of every system?

freddyuk

The bypass pipe work will get very hot and so will the radiator BUT it should not be a radiator within the normal house circuit as it will get scaldingly hot. The person who installed this is not competent to plumb solar systems. The bypass needs replumping in the attic or away from human contact and it needs to be automatically controlled by the system controller. Solar systems do not overheat in summer if they are designed and installed by someone who has a clue. Sadly your system is badly installed. How does your bypass control overheat on a timer? It must be controlled by the temperature of the system so now you are wasting energy and missing out on free hot water all the time the pump is running! Images would help sort it out but you need to redesign and reinstall correctly to avoid expensive damage and potentially scalding burns to anyone who touches the radiator or adjacent pipe work and of course to save money. The plumber who installed this needs to be stopped.