---
title: Pool temperature control over KNX with Pool’nX (hysteresis)
description: "Set up hysteresis control in Pool’nX: setpoint and water temperature read on the KNX bus, heating on/off command and status feedback addresses."
canonical: https://wiki.can-nx.com/en/guides/pool-temperature-control/
language: en
product: Pool’nX
audience:
  - administrateur
  - installateur
context: "Can’nX Cloud, Pool’nX window: Temperature Control"
---

# Pool temperature control over KNX with Pool’nX (hysteresis)

Context: Can’nX Cloud, Pool’nX window: Temperature Control

**Temperature Control** turns Pool’nX into an on/off controller on the KNX bus: it compares the water temperature sent by a KNX sensor with a setpoint, then writes on or off to a command address, for example the address of a heat pump actuator. Control uses only KNX telegrams; it works whatever the type of pool.

Intended for the installer who controls pool heating from KNX.

## Before you start

- A KNX sensor writes the water temperature to a group address, in DPT 9.001.
- A KNX actuator receives the heating on/off command, in DPT 1.001.
- In ETS, plan the addresses for the setpoint and the status feedback, in DPT 9.001 for the setpoint and 1.001 for the control feedback.

## Fill in the control settings

1. In the **Pool'nX** window, next to **Temperature Control**, click the button with the thermometer icon.
2. Fill in the group addresses using the table below, in X/Y/Z format.
3. In **Hysteresis**, enter the difference in °C, for example **1** (example).
4. Turn on **Enabled**.
5. Click **Save**. **Success!** confirms the save.

| Field | DPT | Role of Pool’nX |
| --- | --- | --- |
| **Setpoint** | 9.001 | Receives the setpoint written by the visualization or a KNX button. |
| **Setpoint feedback** | 9.001 | Writes the setpoint at each new value, on save and in response to a read. |
| **Current Temperature** | 9.001 | Receives the temperature written by the sensor. |
| **Control** | 1.001 | Writes 1 to switch on, 0 to switch off. |
| **Control feedback** | 1.001 | Answers read requests with the control state. |

The DPTs are set by Pool’nX: the window only offers the addresses.

## Understand the control logic

At each telegram received on **Setpoint** or **Current Temperature**, Pool’nX compares the two values:

- temperature below the setpoint minus the hysteresis: 1 is written to **Control**;
- temperature above the setpoint plus the hysteresis: 0 is written to **Control**;
- in between: nothing is written, the command keeps its state.

Pool’nX keeps only the integer part of the temperature and the setpoint: 29.8 °C counts as 29 °C. Example: with a setpoint of 28 °C and a hysteresis of 1 °C, heating starts below 27 °C and stops from 30 °C.

Control is only recalculated when a telegram is received: set the sensor to send its measurement regularly.

## Check the result

1. In the ETS group monitor, write a setpoint to the **Setpoint** address: the same value is written to **Setpoint feedback**.
2. Watch the sensor telegrams, then the write of 1 or 0 to **Control** when the temperature leaves the range.
3. Check that heating switches on or off.

## Troubleshooting

| Symptom | Cause and action |
| --- | --- |
| Nothing written to **Control** | **Enabled** turned off, settings not saved or temperature within the range. Check the **Setpoint** and **Current Temperature** addresses. |
| Inconsistent values | The sensor or the visualization does not send in DPT 9.001. |
| No answer to reads of the status feedback | **Enabled** turned off or feedback address not filled in. |

See also [Pool’nX troubleshooting](https://wiki.can-nx.com/en/guides/pool-help/).

French labels: **Contrôle de la température**, **Consigne**, **Retour d'état de la consigne**, **Température actuelle**, **Contrôle**, **Retour d'état du contrôle**, **Hystérésis**, **Activation**, **Enregistrer**.