Please note: This listing is for the interface board only. It has no microcontroller and does nothing on its own. You need a UEDX4646 round AMOLED display module (ESP32-S3), which you buy separately. The HotCirc firmware runs on the display module, and you flash it yourself with ESPHome. Temperature sensors, smart plug and enclosure are not included either.

HotCirc – hot water at the tap, without running the pump all day

HotCirc is a self-learning controller for hot water circulation pumps, built on ESPHome. Two DS18B20 temperature sensors detect when hot water is drawn. From that, HotCirc learns a weekly schedule of 336 half-hour slots (7 × 48) and starts the pump shortly before you are likely to need hot water. So hot water arrives at the tap right away, and the pump no longer runs for hours on a timer.

This interface board connects the UEDX4646 round AMOLED display (ESP32-S3, 466 × 466 px, touch) to the temperature sensors, rotary encoder and button. The board uses fine-pitch SMD parts and comes fully assembled and tested.

What's in the box

• 1 × HotCirc interface PCB, fully assembled and tested

Not included (source separately):

• UEDX46460015-MD50ET display module (1.5″ round AMOLED, ESP32-S3, 16 MB flash, octal PSRAM)
• 2 × DS18B20 temperature sensors (outlet and return)
• ESPHome-compatible Wi-Fi smart plug to switch the pump, e.g. Nous A1T
• Enclosure: STL files for 3D printing (base plate and ring, approx. 27 g of filament) are available free of charge in the repository
• Power supply / USB-C cable

The required Frimware and stl-Files for the housing can be found here: Github

Features

• Self-learning weekly schedule: every detected water draw is learned. Old patterns fade a little each day, so HotCirc adapts when your routine changes
• ECO level: a single value (0–255) sets how aggressively the pump pre-heats. Adjustable with the rotary encoder on the display
• Temperature-controlled pump runs: the pump stops as soon as hot water reaches the return pipe (8 minutes maximum as a safety limit)
• Disinfection support: detects the boiler's anti-legionella cycle and flushes the entire loop
• Vacation mode: pauses automatically after 24 h without a water draw
• Anti-seize protection: short weekly pump run, even while the pump is disabled
• Energy tracking: energy transferred and run time per pump cycle

Display and controls

• Round AMOLED display in a smart-thermostat style: ECO ring, outlet and return temperatures, animated pump icon
• Color shows the operating state: blue (standby), orange (pump running), magenta (disinfection), grey (disabled)
• Heatmap page showing the learned weekly matrix, opened with a tap
• Rotary encoder, touchscreen and hardware button
• Three-stage dimming to protect the AMOLED against burn-in

Integration

• Native Home Assistant integration via the ESPHome API, including a heatmap card for Lovelace dashboards
• Built-in web interface on the device
• Wi-Fi setup through a captive portal, no secrets.yaml required
• The pump is switched through an ESPHome smart plug over HTTP, with automatic reconciliation of the relay state

Connections on the board

• 2 × 1-Wire for DS18B20 (outlet GPIO39, return GPIO40, one sensor per bus, no address configuration needed)
• Rotary encoder (GPIO5/GPIO6)
• Sensor connector type JST PH2
• Power supply: USB-C

Firmware

The interface board has no microcontroller of its own. The firmware runs on the ESP32-S3 of the UEDX4646 display module, which you buy separately and flash yourself with ESPHome (esphome run esphome-hotcirc_uedx4646.yaml). Source code, instructions and Home Assistant files: https://github.com/STB3/esphome-hotcirc

Interactive display simulator (try it in your browser, no hardware needed):

https://stb3.github.io/esphome-hotcirc/hotcirc_simulator.html

Requirements

• UEDX4646 display module (not included)
• A recent ESPHome release
• A hot water circulation loop with a pump that can be switched through a smart plug
• Basic ESPHome skills (compiling and flashing firmware)

License

Software: GPLv3. Hardware design: CC BY-NC-SA 4.0. This board is sold directly by the designer.

Safety note

The board operates on low voltage only. Mains voltage is switched solely by the separate smart plug. Any work on the building's plumbing or electrical installation must be carried out by qualified professionals.

For customisable products (e.g. housing part colour or special firmware versions), I'll ask you to make your choice before shipping.

Orders are shipped via DHL / Deutsche Post – Warenpost Premium (tracked) from Germany.

Processing Time Orders are dispatched within 7 business days of payment confirmation.

Delivery Time Once shipped, delivery typically takes 7–15 business days, depending on your location and local postal services. Please note that this is an estimate and not a guarantee.

Tracking A tracking number will be provided once your order has been handed over to DHL / Deutsche Post.

Customs & Import Duties For shipments outside the European Union, customs fees, import duties, and taxes may apply. These charges are the sole responsibility of the recipient. We have no control over customs processing times, which may cause additional delays beyond the estimated delivery window.