My home came with a D’Mand Kontrols S3-100 recirculating hot water pump and controller. I’d like to make my hot water recirculation ‘smart’. However, this is out of my comfort zone so I have no idea what the most cost efficient way to get this controllable by HA.
From a very brief web search and superficial read, it looks like it is easily possible to control it with a button press. One is offered as a vendor option.
Add a relay to HomeAssistant, and use the outputs as a button with a ahort activation time should be all you need to make it smart. Even a cheap simple ESP8266 type relay device should do the job. Maybe incorporate a waterproof temperature sensor like the DS1820B you can zip-tie to the water pipe for more data. Add two if you like, as one input pin can support more than one sensor through the OneWire technology which supports long wiring runs with the addition of one simple resistor Just use a spare pin from the device and configure appropriately in ESPHome for the temperature sensors as an input as well as the button/relay as an output.
Configuring a thermostat type situation in HomeAssistant should take care of the rest. You decide your temperature trigger thresholds, pump ‘on’ and ‘off’ time/duration, monitor the logs and graphs, and tweak accordingly.
Hints: For best electrical isolation, use a relay with ‘dry contacts’ which are independant of the other electronics (most are, even the cheapest. If you can see a relay in the photo in the advert, you are fine. Just use the NO - normally open - ones in place of the button wiring connection).
Just guessing: If you closely read the specifications, you may even be able to use the existing power supply to power your relay board. Just match the voltages and make sure there is enough current to drive the relay board. Around 500mA minimum (0.5A) should be enough for most relay boards. Watch you don’t mix 5v, 12v, and 3.3volts if you wish to avoid smoke!
As it is close to water, putting it all in a waterproof case is recommended for safety reasons.
Good luck. Feel free to post your code and specifications you are looking at if you need any more pointers.
Be sure to post your progress, and pictures, as there may be many others that are also facing the same requirements.