Looking for something to add to the geyser to monitor the water temperature.
Something simple and easy but preferably a unit that can transmit the temp through an app of sorts.
Hoping for something that one can just stick to the side of the geyser which will measure the wall temp, makes some calculated assumptions/adjustments as to what the water temp would likely be and transmit that.
Surely there is something like that? What do you guys use?
I connected 2 DS18B20 sensors to a D1 mini, and stuck them onto the geyser, just above and below where the element goes in.
I then average the 2 readings in HA.
I found sticking it to the wall wasn’t great, since geysers are generally double-walled so you’re not getting a good reading. Sticking it close to where the element goes in gave me much better readings.
You can see in the graph below (dark background is when geyser is on), how well the sensors track.
So, not plug and play, but it does the job.
Sonoff Th16 can do that for you. I’m running one on my geyser to check the temp. It’s controlling a contactor that’s connected to my Solar power side.
I already got a probe in the geyser that gives the info to the geyserwise unit, so I’m running the th16 probe on the top part of the gesyer where the warm water go’s in form the Solar geyser park. It gives the closes reading to the temp inside the geyser for me.
My Sonof Th16 is on the way to do exactly this as well.
Just for those who do not know. The DS18B20 is the same as the cable that comes with the TH16 (if you don’t take the humidity+temp sensor) and the D1 mini runs of the same chip as the Sonoff just without the 220V to 5V built in. So these 2 options are basically the same (just 220V vs 5V).
Are you guys running Tasmota, ESPHome or something else?
I’m not so advance with programming 
Still need to get my hands in to it and learn to do home automation part. Will do this with the bigger house we moving in. Got a Shelly setup to.
Running EspHome.
I like it because you can just define the device using yaml (and then share that yaml if you want).
I know some people prefer Tasmota, and there are arguments for both, but I’ve gotten quite used to Esphome, so will stick with it for now.
Please give a little more info? That probe, is drilling required to get it into the geyser? Where exactly does that Sonoff unit go? In your db?
What do you mean its connected to your solar side? Sorry, complete noob with this.
I don’t even know what a D1 mini is lol. Please can you give a little more info, or even photos would be great.
Do I absolutely have to have Home Assistant to make use of the D1 and its sensors?
Don’t want any Tasmota or Yaml or Node Red or any of that foreign Greek concepts. Looking for something plug and playish.
You open the plastic cover of your geyser. There you will find your heating element and the electrics of that. The element is inserted into a tube into the geyser and fastened with a flange plate. There is also a temp sensor for the element.
Just stick the sonoff temp sensor inside where the current sensor is if you can, else paste it to the flange plate.
The Sonoff needs power to operate, but you can put it anywhere out of the weather. It’s too big for a DB.
Stick to to Sonoff. It has a case and power sorted. The D1 mini is for people that want to play around and have none of those.
None of these things is plug and play. You will have to go buy an expensive system for that 
So, the flanch is used to house the Sonoff’s probe, and the geyser element goes through it as well? So the whole shebang, geyser drained to accomplish this?
And the Sonoff can get its power from the circuitry that powers the geyser right there and then?
This Sonoff also have built in wifi which I must setup with my network?
Thanks Louis. I always assumed you’ll need to remove the mechanical thermostat and replace it with something electronic which I wasn’t really comfortable with, but this would be perfect.
In my case (still toying with the idea in my head) I’m looking at doing something along the lines of powering the geyser only during certain hours to have it only heat up using PV, and set the thermostat to something higher like 70C / 75C or whatever is allowed and using have a contactor to switch it off if the water temperature is higher than 55C and the batteries starts to be used.
The flange is what the current components use. Don’t remove them. If you can add the probe to existing stuff then do that. Else just paste it to it on the outside. Check your geyser’s manual. The current temp measurement is normally in a waterproof tube that you can swop out without draining the water.
It just needs 220V, so yes. But a normal geyser will draw too much current so switching those through the Sonoff TH16 is not recommended. The TH16 has a 15A relay, but the connections are small which is a problem with that current. I have a heat pump that use only 900W, so that is much better. For a normal geyser element you will need a bigger relay (which you can power from the Sonoff). Search these forums - this has been discussed before.
Yes it works on your Wifi (the normal 2.4GHz, not 5GHz). The Sonoff can be controlled with their normal app(it should tell you the temp and you can switch the relay on/off), which will also assist you in the setup on your Wifi. If you want to do more then you flash it with Tasmoto or ESPHome, hook it up to Node-Red or HomeAssistant and off you go.
My Heatpump came with the instructions to paste it like this. It’s been running for 3+years like that and works well. The old thermostat is for the backup element.
If only GeyserWise would create an API for their device. Would be a perfect solution.
Louis gave most of the answers. Thanks 
I got a solar geyser that is controlled by Geyserwise setup. What I did was, I got 2 contactors that interlock. the gesyerwise element output is connect on one side of the Contactor and controls that part when you press the warm switch on button on the geyserwise keybad. then on the second contactor I got my Solar power connected to with the Sonoff th16. the th16 controlls the contactor 2.
So in the winter the sun in cape town isn’t so warm so it takes longer for the solar geyser to warm, so after my batteries is fully charge, then I dump the extra solar power to my geyser for a hour or hour and half to warm it up nicely.
Why the interlock. say my wife press the geyserwise warm button and I don’t know about it and i press the th16 on, then the interlock locks out the part that switch on last, so i can’t pushed my solar power back in to the grid.
Will check it out. Thanks
Much obliged Louis!
Indeed. There is a pocket where the thermostat sits, and the terminals to the element sits on either side of it. The thermostat itself has a long prong going into this pocket, and two terminals that connect to the element as you push it in. Then the wiring connects to the back of the thermostat. You can replace the whole shebang without draining the geyser.
Some heat pumps have a retrofit sensor with a really thin wire that you slide down to the bottom of this tube, while leaving enough space so that the original thermostat can still sit inside the same tube (being careful to nick said thin wire of course).
If you are not using the thermostat, I would think you could pull it out and put the heat sensor connected to your sonoff down the same hole. With or without the heat pump’s sensor (if you have that).
Otherwise, you can also just put it right against the flange. Heck you could probably put it under the lagging on the pipe at the top/bottom too and you’d get a reading, since the piping itself leaks some of the heat. You’d just not get an accurate reading, since the moment you use any hot water the bottom goes ice-cold immediately, while the top may remain hot right until the last hot water is consumed 
My idea is to stick that probe somewhere on the geyser where at least a warmer than ambient reading will result. Lets say my geyser heats to 60 degrees and this reading is 40 when it switches off having reached temp.
If this 40 reading is fairly consistent, then I know my geyser is at 60 degrees when the probe tells me 40.
All I really want is some way of knowing how long the geyser still has to go to reach its set temp.
