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The Hot Water sensor CS92 has suffered from a bug since the very beginning. You may have noticed your Fault Log full of Hot Water comms failure and restore messages.
In the early days it was thought to be an issue with the battery contacts and tightening them seemed to solve the problem.
Then it was thought it was an issue with the battery levels themselves and so frequent fresh batteries were the answer.
I attempted to solve both these by running my CS92 using the same PSU as used for the controller, juat stepped down to 3.2V.
However the real issue is that in order to conserve battery, the CS92 transmits very very infrequently when its not in a Hot Water heating schedule block. These messages can sometimes be missed by the controller and then it reports a comms failure until the next message is received that could be many hours aways.
This is another reason why the Hot Water sensor seems to work fine when in actual operation, because then there are more frequent updates.
However during the summer months, my Hot Water is almost never managed by Evohome and so the errors are a near daily occurrence.
Until a better Hot Water sensor is developed or introduced, here is my solution. It's clumsy and horrible, but works.
Given I used a PSU to power by CS92, I just added a networked Relay to the power inputs.
Using Home Assistant and ramses_cc, I can check if the Hot Water schedule is current or not. If Evohome is not in a Hot Water ON mode, I simply reboot the CS92 every 30mins. This forces the CS92 to take a Hot Water temperature reading and transmit it. And that stops my errors. I took inspiration from the early experiments of pulling the batteries out. This does the same thing, except via automation.
Residio, if you are still reading these forums, even in 2025 you would still get some repeat business if you finally decided to introduce a mains powered version of the CS92, without any of the battery management features. 99% of installs will have accessible power near the Hot Water tank. Do it.
In the early days it was thought to be an issue with the battery contacts and tightening them seemed to solve the problem.
Then it was thought it was an issue with the battery levels themselves and so frequent fresh batteries were the answer.
I attempted to solve both these by running my CS92 using the same PSU as used for the controller, juat stepped down to 3.2V.
However the real issue is that in order to conserve battery, the CS92 transmits very very infrequently when its not in a Hot Water heating schedule block. These messages can sometimes be missed by the controller and then it reports a comms failure until the next message is received that could be many hours aways.
This is another reason why the Hot Water sensor seems to work fine when in actual operation, because then there are more frequent updates.
However during the summer months, my Hot Water is almost never managed by Evohome and so the errors are a near daily occurrence.
Until a better Hot Water sensor is developed or introduced, here is my solution. It's clumsy and horrible, but works.
Given I used a PSU to power by CS92, I just added a networked Relay to the power inputs.
Using Home Assistant and ramses_cc, I can check if the Hot Water schedule is current or not. If Evohome is not in a Hot Water ON mode, I simply reboot the CS92 every 30mins. This forces the CS92 to take a Hot Water temperature reading and transmit it. And that stops my errors. I took inspiration from the early experiments of pulling the batteries out. This does the same thing, except via automation.
Residio, if you are still reading these forums, even in 2025 you would still get some repeat business if you finally decided to introduce a mains powered version of the CS92, without any of the battery management features. 99% of installs will have accessible power near the Hot Water tank. Do it.
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