Geyserwise Temperature under (or delayed) reading?

V

Vnr

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Hi all,

I've recently installed (horizontal) a new 150l geyser (https://www.ariston.com/en-za/products/electric-water-heaters/electric-storage/axios-geyser) and replaced the 3kW element with a 2kW element. I want to heat the geyser primarily when I'm producing more solar than my house and batteries can accept.

I bought a Geyserwise TSE for temperature measurement - the plan is to replace the display unit with a Geyserwala Connect so I can get the reading via MQTT into HA/similar. But I'm having a problem with step 1 of the process... getting a temperature reading that I can trust. It seems to me that the reading from the thermistor is often less than the reading at the hot water outlet. I "understand" that the probe is near the cold water inlet of the geyser, and the potential issues around stratification, but I'm hoping you could explain the following behaviour that I'm seeing:

- As soon as I use hot water, the temperature reading drops to around 20 degrees C. I'm guessing this is because the probe is located near the cold water inlet.
- When the geyser is heating, the temperature rises fairly slowly. I have a CBI Astute in line with the geyser, so I'm able to use the temperature reading in conjunction with the power consumption reading and the specific heat equation to verify that the temperature reading is lower than expected
- When the Geyserwise turns off power (at the setpoint 55 degrees) the temperature continues to rise for 1.5 to 2 hours later. For example, on one day the element turned off at 14:55 (temperature was 55 degrees) but it continued rising until it read 65 at 17:25.
- All the above I can deal with and factor in when I get to my HA implementation. My major issue is that on more than one occasion in the last 2 weeks, with the temperature setpoint at 55 degrees C, my TP valve opened. This appears to confirm that the reading at the Geyserwise probe and the actual water temperature near the TP valve is very different.

Has anyone else experienced this? If I understand correctly, this means that the 90 degrees mechanical cutout is ineffective for my setup, because the TP valve is venting before the thermostat cuts out?

I've had two different installers come out to confirm that the probe is correctly inserted and pushed in all the way. I've even bought a new Geyserwise probe to replace the original (which was only 3 weeks old anyway...) just in case there was an issue, and it has vented at least once since the probe was replaced.

I'm at the point where I'm considering putting the original thermostat back in, so that it least power cuts out before the TP valve opens. And then look for another place to measure the temperature with the Geyserwise probe.

Has anyone experienced something similar? I'm wondering if it has something to do with my geyser construction (forgive my ignorance). Would you recommend putting the probe into the "renewable energy port" in this geyser, or is there a way to put it at the outlet?

Thanks!
 
For whats its worth my Geyserwise controller in my solar/electric geyser can only turn on the power to my geyser before the thermostat. The max temp on electrical power is set by the geyser thermostat and can't go above 55C on electric power. The solar tubes can push it much further depending on the irradiation of tubes

That said the temp seems to exactly match the geyser thermostat as it holds a perfect 55%C according to the geyserwise controller
 
Vnr said:
Hi all,

I've recently installed (horizontal) a new 150l geyser (https://www.ariston.com/en-za/products/electric-water-heaters/electric-storage/axios-geyser) and replaced the 3kW element with a 2kW element. I want to heat the geyser primarily when I'm producing more solar than my house and batteries can accept.

I bought a Geyserwise TSE for temperature measurement - the plan is to replace the display unit with a Geyserwala Connect so I can get the reading via MQTT into HA/similar. But I'm having a problem with step 1 of the process... getting a temperature reading that I can trust. It seems to me that the reading from the thermistor is often less than the reading at the hot water outlet. I "understand" that the probe is near the cold water inlet of the geyser, and the potential issues around stratification, but I'm hoping you could explain the following behaviour that I'm seeing:

- As soon as I use hot water, the temperature reading drops to around 20 degrees C. I'm guessing this is because the probe is located near the cold water inlet.
- When the geyser is heating, the temperature rises fairly slowly. I have a CBI Astute in line with the geyser, so I'm able to use the temperature reading in conjunction with the power consumption reading and the specific heat equation to verify that the temperature reading is lower than expected
- When the Geyserwise turns off power (at the setpoint 55 degrees) the temperature continues to rise for 1.5 to 2 hours later. For example, on one day the element turned off at 14:55 (temperature was 55 degrees) but it continued rising until it read 65 at 17:25.
- All the above I can deal with and factor in when I get to my HA implementation. My major issue is that on more than one occasion in the last 2 weeks, with the temperature setpoint at 55 degrees C, my TP valve opened. This appears to confirm that the reading at the Geyserwise probe and the actual water temperature near the TP valve is very different.

Has anyone else experienced this? If I understand correctly, this means that the 90 degrees mechanical cutout is ineffective for my setup, because the TP valve is venting before the thermostat cuts out?

I've had two different installers come out to confirm that the probe is correctly inserted and pushed in all the way. I've even bought a new Geyserwise probe to replace the original (which was only 3 weeks old anyway...) just in case there was an issue, and it has vented at least once since the probe was replaced.

I'm at the point where I'm considering putting the original thermostat back in, so that it least power cuts out before the TP valve opens. And then look for another place to measure the temperature with the Geyserwise probe.

Has anyone experienced something similar? I'm wondering if it has something to do with my geyser construction (forgive my ignorance). Would you recommend putting the probe into the "renewable energy port" in this geyser, or is there a way to put it at the outlet?

Thanks!
Click to expand...
Are you certain its the tp valve opening and not the op regulator on the inlet side
 
I noticed exactly the same.
After 2 showers the geyserwise shows 19°C.
I have the PV/AC combination geyserwise conversion kit. Previous geyser only lasted 4 years before bursting.
 
soulie said:
Are you certain its the tp valve opening and not the op regulator on the inlet side
Click to expand...
I don't fully understand the plumbing around the geyser, but two pipes are coming out of the ceiling, one which I think is connected to the drip tray (PVC?) and one which is copper. The water that comes out is from the copper pipe and is steaming hot.

Since I posted earlier today, I left the house and when I returned now it's apparent (from the water outside the house) that it vented again :crying:

This is after I dropped the Geyserwise setpoint to 50 degrees last night, hoping that this will prevent the temperature from getting anywhere close to causing venting.

The knock-on negative effect of all this is that because the geyser tops up with cold water when it vents, the temperature immediately drops to approx. 20 degrees and it continues heating. So, in the 5-hour operating window that I've configured (11:00-16:00), the geyser was on the entire time (which I can confirm because the CBI recorded 10.6kWh of consumption today). So much for only wanting to use excess solar energy for this!

Right now (17:00) the geyser temperature is reading 24 degrees after 10kWh consumption... I understand it's likely because of the cold water that replaced the hot water that vented, but this is my problem - if I look at the reading, I have no way of understanding whether it's low because it just filled, or it is low because the entire body of water is at that temperature.

Of course, my biggest concern is safety - I'm definitely thinking of going the route of @Tim_vb, to put the original thermostat in, but I was really hoping to get some validation as to this being something others have seen. I've spoken with Geyserwise and they say that they haven't experienced this before and that I should send photos of the installation (which I will do), but it's unlikely (possible but unlikely) that two independent plumbers (whom I paid to check) would tell me that the first installer did the job correctly if it wasn't correctly installed. And then, I still want to read the temperature fairly accurately so that I can know, when I implement HA, whether the reading I see is fairly close to the hot water experience in the shower...

Some additional information - I tracked the temperatures and power consumption periodically over the past two days (when the setpoint was 55 degrees). Took these readings manually because I don't want to put the Geyserwala Connect in yet (in case Geyserwise washes their hands off this because I modified it)

Wednesday 03 July
08:15 27degreesC
09:02 27
10:28 27
11:00 27 *geyser turned on
11:30 28
12:02 30
13:16 39
13:36 43. 5.51kWh used so far. According to specific heat, this should be 58.63 degrees
14:51 55. 8.12kWh
14:56 56. 8.21kWh. Geyser stopped heating. According to specific heat, this should be 74.12 degrees
15:13 58. Temp rising despite being off.
15:20 59
15:46 60
17:26 62
21:18 65

Thursday 04 July
05:45 56
07:09 53
07:40 26 - after first shower
08:01 19 - after second shower
12:16 28
15:04 50. 8.83kWh. Pressure valve opened. According to specific heat, this should be 79.23 degrees
15:51 24. Because the pressure valve opened.

Thanks for all your suggestions thus far!
 
Vnr said:
I don't fully understand the plumbing around the geyser, but two pipes are coming out of the ceiling, one which I think is connected to the drip tray (PVC?) and one which is copper. The water that comes out is from the copper pipe and is steaming hot.

Since I posted earlier today, I left the house and when I returned now it's apparent (from the water outside the house) that it vented again :crying:

This is after I dropped the Geyserwise setpoint to 50 degrees last night, hoping that this will prevent the temperature from getting anywhere close to causing venting.

The knock-on negative effect of all this is that because the geyser tops up with cold water when it vents, the temperature immediately drops to approx. 20 degrees and it continues heating. So, in the 5-hour operating window that I've configured (11:00-16:00), the geyser was on the entire time (which I can confirm because the CBI recorded 10.6kWh of consumption today). So much for only wanting to use excess solar energy for this!

Right now (17:00) the geyser temperature is reading 24 degrees after 10kWh consumption... I understand it's likely because of the cold water that replaced the hot water that vented, but this is my problem - if I look at the reading, I have no way of understanding whether it's low because it just filled, or it is low because the entire body of water is at that temperature.

Of course, my biggest concern is safety - I'm definitely thinking of going the route of @Tim_vb, to put the original thermostat in, but I was really hoping to get some validation as to this being something others have seen. I've spoken with Geyserwise and they say that they haven't experienced this before and that I should send photos of the installation (which I will do), but it's unlikely (possible but unlikely) that two independent plumbers (whom I paid to check) would tell me that the first installer did the job correctly if it wasn't correctly installed. And then, I still want to read the temperature fairly accurately so that I can know, when I implement HA, whether the reading I see is fairly close to the hot water experience in the shower...

Some additional information - I tracked the temperatures and power consumption periodically over the past two days (when the setpoint was 55 degrees). Took these readings manually because I don't want to put the Geyserwala Connect in yet (in case Geyserwise washes their hands off this because I modified it)

Wednesday 03 July
08:15 27degreesC
09:02 27
10:28 27
11:00 27 *geyser turned on
11:30 28
12:02 30
13:16 39
13:36 43. 5.51kWh used so far. According to specific heat, this should be 58.63 degrees
14:51 55. 8.12kWh
14:56 56. 8.21kWh. Geyser stopped heating. According to specific heat, this should be 74.12 degrees
15:13 58. Temp rising despite being off.
15:20 59
15:46 60
17:26 62
21:18 65

Thursday 04 July
05:45 56
07:09 53
07:40 26 - after first shower
08:01 19 - after second shower
12:16 28
15:04 50. 8.83kWh. Pressure valve opened. According to specific heat, this should be 79.23 degrees
15:51 24. Because the pressure valve opened.

Thanks for all your suggestions thus far!
Click to expand...
dont stress over temp values ,they are meaningless , the pressure regulator releases hot water at the geysers pressure rating ie 600 kpa , the only way it can release is if its too hot causing excess pressure , the tp valve will empty half your geyser if activated , drop your temp by 2 deg at a time untill it stops doing funky things then start monitoring the temps , when it stops dripping then the temp is ok . you will also hear the tp valve release it sounds like a freight train sometimes , your geysers hysteresis curve may take some getting used to , but you will eventually work out the happy temp ,( as long as the op regulator is new and right for the geyser ie correct pressure then you are safe )if regulator isnt new or is incorrect value ,replace it , )
 
Thanks for this explanation! I will get a plumber in to replace the op regulator - I suspect that's the one where the cold water comes into the house (and thus into the geyser) - it can only be about 4 years old, but to be safe I will get it checked and changed.

I still have the problem that I don't know what setpoint to set the Geyserwise to. Based on today's experience, 50 degrees is too high.
 
Tim_vb said:
For whats its worth my Geyserwise controller in my solar/electric geyser can only turn on the power to my geyser before the thermostat. The max temp on electrical power is set by the geyser thermostat and can't go above 55C on electric power. The solar tubes can push it much further depending on the irradiation of tubes

That said the temp seems to exactly match the geyser thermostat as it holds a perfect 55%C according to the geyserwise controller
Click to expand...
I'd feel a lot more comfortable if I put the original thermostat back in and set this to 55 as you have. Where did you put your Geyserwise probe?
I don't have any solar heating/heat pump in my system, which is why I thought perhaps I could use the renewable energy port for the Geyserwise probe.
 
Vnr said:
Thanks for this explanation! I will get a plumber in to replace the op regulator - I suspect that's the one where the cold water comes into the house (and thus into the geyser) - it can only be about 4 years old, but to be safe I will get it checked and changed.

I still have the problem that I don't know what setpoint to set the Geyserwise to. Based on today's experience, 50 degrees is too high.
Click to expand...
Personally i would put the regulator as close to the geyser as possible and remove the one outside ,its a kak design and can create issues ,the regulator has cold in ,cold out to the geyser and a overtemp outlet with thingy screwed into it which is colour coded or marked with kpa .you can also sometimes leave the old one be and ask him about a new one at geyser ,depends on how the system is plumbed in .
 
Vnr said:
Thanks for this explanation! I will get a plumber in to replace the op regulator - I suspect that's the one where the cold water comes into the house (and thus into the geyser) - it can only be about 4 years old, but to be safe I will get it checked and changed.

I still have the problem that I don't know what setpoint to set the Geyserwise to. Based on today's experience, 50 degrees is too high.
Click to expand...
Also have a look on the geyser itself one of the rating plates may give the max working temp ,some are 60c set temp at 10% less untill youve worked things out .
 
Vnr said:
I'd feel a lot more comfortable if I put the original thermostat back in and set this to 55 as you have. Where did you put your Geyserwise probe?
I don't have any solar heating/heat pump in my system, which is why I thought perhaps I could use the renewable energy port for the Geyserwise probe.
Click to expand...
I'm not sure where its placed as I only went into my roof once and that was enough for me lol

The renewable port could be port used to monitor the temp of the solar tube array and trigger the pump to circulate the water back into the geyser. have a look at the install manual for your model
 
Thanks for your help guys. I'll try and keep this thread updated as and when things happen, in case someone else experiences something similar down the line. I'm going to follow the suggestion from @soulie to put in a regulator closer to the geyser. I'm also going to do as @Tim_vb recommended and put the original thermostat back in.

I'm going to chat with the local Plumblink guys to find out whether there are any other ports in my geyser that I can use to put the Geyserwise thermostat in (for temperature reading only, and not for control). I am a bit disappointed that the Geyserwise thermostat does not function properly to control the temperature - I could have just gone the route of a DS18B20/similar but I wanted something reputable. I just can't trust that Geyserwise can control the geyser temperature without it boiling over (it boiled over again yesterday after 3 days without issue at the setpoint of 50 degrees).

PS I checked the operating/working temperature of the geyser and it is 70 degrees. I asked the Geyserwise support guy about this and he said that it's because the original thermostat has a maximum setting of 70 degrees, which checks out. He also says that their thermostat will cut off if the temperature gets to 90 degrees...
 
Last edited:
An update on this issue. I put the original thermostat back into the geyser and set it to 60 degrees. I then removed the NTC sensor from the tip of the Geyserwise thermostat and strapped it to the geyser outlet pipe (put it under the insulation/lagging).

I increased the setpoint on the Geyserwise unit to 75 degrees to allow for the fact that the Geyserwise sensor is measuring the temperature at the outlet which may be hotter than the inlet side of the geyser. The thinking is that the thermostat will control the heating up to its setpoint of 60 degrees.

Since making these changes, the reading is far more accurate - I would say there's a maximum discrepancy of 5 degrees between the thermostat and the sensor, based on the fact that when Geyserwise is reading between 70 and 75 degrees (i.e. just before it turns off the power) the thermostat switches off the power to the element (I can detect this with the power consumption on the CBI Astute). No more TP valve opening while heating for the last week!

In my thinking, there are two possibilities as to why the previous configuration didn't work:
1. In order to remove the sensor from the Geyserwise thermostat, I had to cut and rejoin the sensor cable. In doing so, I removed a small portion of the cable, around the point where the cable comes out of the thermostat. Perhaps the cable was previously damaged at that point (there is a possibility that is can get pinched where it comes out of the thermostat). If this was the issue, then it means that both the Geyserwise thermostats that I fitted (which both behaved similarly) suffered from the same problem.
2. The Geyserwise thermostat was not able to accurately read the temperature in my geyser, perhaps because it is slightly shorter than the original geyser thermostat. Maybe the air gap is too large to get an accurate reading? According to the Geyserwise technician, this is unlikely because they would have had issues with other customers who have the same geyser.

Just thought I'd put my findings down for the next person who has a similar issue. I'm comfortable with the current setup because the original geyser thermostat is ultimately protecting the geyser from overheating.

Next step is to install the Geyserwala Connect! Again, thanks for all the input!
 
Vnr said:
An update on this issue. I put the original thermostat back into the geyser and set it to 60 degrees. I then removed the NTC sensor from the tip of the Geyserwise thermostat and strapped it to the geyser outlet pipe (put it under the insulation/lagging).

I increased the setpoint on the Geyserwise unit to 75 degrees to allow for the fact that the Geyserwise sensor is measuring the temperature at the outlet which may be hotter than the inlet side of the geyser. The thinking is that the thermostat will control the heating up to its setpoint of 60 degrees.

Since making these changes, the reading is far more accurate - I would say there's a maximum discrepancy of 5 degrees between the thermostat and the sensor, based on the fact that when Geyserwise is reading between 70 and 75 degrees (i.e. just before it turns off the power) the thermostat switches off the power to the element (I can detect this with the power consumption on the CBI Astute). No more TP valve opening while heating for the last week!

In my thinking, there are two possibilities as to why the previous configuration didn't work:
1. In order to remove the sensor from the Geyserwise thermostat, I had to cut and rejoin the sensor cable. In doing so, I removed a small portion of the cable, around the point where the cable comes out of the thermostat. Perhaps the cable was previously damaged at that point (there is a possibility that is can get pinched where it comes out of the thermostat). If this was the issue, then it means that both the Geyserwise thermostats that I fitted (which both behaved similarly) suffered from the same problem.
2. The Geyserwise thermostat was not able to accurately read the temperature in my geyser, perhaps because it is slightly shorter than the original geyser thermostat. Maybe the air gap is too large to get an accurate reading? According to the Geyserwise technician, this is unlikely because they would have had issues with other customers who have the same geyser.

Just thought I'd put my findings down for the next person who has a similar issue. I'm comfortable with the current setup because the original geyser thermostat is ultimately protecting the geyser from overheating.

Next step is to install the Geyserwala Connect! Again, thanks for all the input!
Click to expand...
Thanks for the update.
Do you perhaps have a picture of the modifications?
I am thinking of doing the same.
 
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