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Can I switch my geyser off?


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I have a solar geyser with a Geyserwise meter attached to it. . During a normal jhb summer's day, the water quite easily goes from about 30 in the morning to 55-60 by the evening. In winter, it goes from about 20 in the morning to 45 in the evening so I had the element on for about an hour to take it to 65.


During winter, I wasn't home for a week and I 'switched the geyser off' using the function on the Geyserwise monitor. However, when I returned home the water temperature was 91! I think the pump still ran when the sun was out even though the monitor said "off". I'm going on holiday for a month soon and I'm really worried that the geyser will explode or something as I don't know how to stop it from generating heat when the sun is out. Does anyone know how to switch it off?

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Even if switched off at the mains the solar pump still runs when the sun is out. One day I had no water and I tried switching the mains off but the pump was just making a huge noise trying the pump nothing. 


All it says on it is GeyserWise Max

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I have a Solar Geyser with a "Geyserwise Max" controller - its "Away/Holiday Mode" works well when you don't want your geyser to overheat.  Your press the outer two buttons at the same time to engage this mode - and it displays a small "OFF" icon.  Eskom power is never used in this mode.

The "Away/Holiday Mode" turns on the circulation pump at night to cool the Geyser down to 50C. This ensures that the geyser starts off every morning at a maximum of 50C.

If this is not working, then you may have a blocked filter in series with the circulation pump.

EDIT: If you turn off your water main while away, the geyser can loose some water via the expansion valve and circulation pump can stop working - leading to very high temperatures in the collector.

Edited by NigelL
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Thanks @Vassen! You've got this spot on! I have tubes on my roof and when the water gets very hot (over 75), I get lots of water leaking down my roof! I also have a 12v pump so switching off the electricity supply does nothing.


I was actually afraid of the cover up suggestion as there is no way for me to access my roof without getting contractors in. Guess I'll just have to take a chance that the valve is working

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Go and buy yourself a timer at builders. It is cheaper other places and install it.
You can program it to suit your requirements.  Cost +/- R360. Other stuff is making others rich.
You don't need fancy stuff. Rather spend your $ on vacuum tubes than fancy timers

This is mine one for my pool and one for the geyser.image.thumb.png.819062954713a389c0c60248db781055.png

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  • 2 weeks later...
On 2020/12/03 at 10:29 PM, Vassen said:

Sorry, but I think you missed the opening post or maybe I’m very confused.  He has a solar geyser (tubes) and that’s the problem. I don’t see how this timer is going to resolve that. There’s no way to stop the tubes from boiling water other than covering it or somehow cooling it down by running the pump during the night. 

Yes I missed that.

I have never seen water been boiled by normal solar geysers. The most is 85deg unless you have an over designed system.  Then I would rather add a second reservoir and use them in tandem.

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19 minutes ago, Vassen said:

Here’s a quick video that shows water boiling in a tube. You can do a quick search and can find others as well. 

Flat plate solar collectors will get water to around 70 degrees at max if I remember correctly and can then be switched off and will not heat any further. 

The heat pipe in an evacuated tube can easily get beyond 130 degrees easily. I’ve installed mine myself and know it gets untouchable very quickly after being exposed to a little sun. I’ve read of some that can even get to 200 degrees. The heat pipe then goes into a manifold and water flows through the manifold and gets heated as it flows through. If the water does not circulate, it will continue to heat until it gets to almost the same temperature of the heat pipe minus the transfer losses. 

Most 200l evacuated tube systems are designed with 20-24 tubes. Even with a second reservoir, if the water is not used for extended period of time, it will boil and be released through the pressure release valve. My 200l system can take the temperature from 40 degrees to 80 degrees on a good clear day. On the second day, it’s going to go beyond 100 and vent.   


I should learn to answer with a little more words.  I full accept that water boils in  vacuum tube.  I only have 10 tubes so I never heat up to full temp.

But a second reservoir works nice.


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8 hours ago, Vassen said:

Okay no worries. 

have you left your 10 tubes open when you’ve gone away for a few days. 

I’ve installed mine around April this year and always cover the tubes when I go away for more than a day.  Don’t want to take a chance 

My tank has a pressure relieve valve. At +/- 1.2 bar it blows as it is a fiber tank. This feeds into a 200l geyser.  I only do this to increase the amount of hot water. Never gave boiling point a thought. The few pipes heats the water to a max of 85C.  The pump is driven by solar so its only off during the day when it is faulty.
Check if your geyser have a pressure relieve valve.  This is to safeguard the geyser.
What should happen is when boiling point is reach the pressure in the tank should blow out and allow a bit of cold water to enter,  In certain areas the water pressure can go higher than 4 Bar at 2 bar pressure the boiling point is increased to +/- 125C.
Have you ever experienced a blow out?
Do you know what pressure your geyser can handle? 
Make sure that the pressure relieve valve its @ 2.5B and its not to high for the tank. Else at 100C and +/-1.2B it should start relieving that I have never  see or heard of happening. At 1,5B the boiling temp is +/- 115C.

The pressure relive valve will let the hot water go if it generates steam as steam relates to pressure. If you are in an area where the pressure is > 3B then boiling point is even higher.

Increase the pressure and you increase boiling point .5B makes a difference. Geysers pops because of the water pressure increasing and then its normally because the pressure relieve valve is stuck (rust) or the regulator valve packs up through aging....

Would love to be proven wrong but I do not believe you are going to reach 115C if any person has these fancy temp monitors on their geysers would love to see the max C it reaches. 115C is a little far away for a few pipes and 200l tank

Edited by Erastus
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