---
title: "Temperature Hysteresis Controller"
description: "Temperature hysteresis controller in TapHome: when the relay switches on and off, how a valve follows the Plus, Minus or Middle band, floor protection and an interactive simulator."
url: "https://taphome.com/en/docs/smart-rules/hysteresis-control/"
language: en
lastmod: 2026-11-11
generator: hugo
ai:
  topics: ["smart-rules","hysteresis-controller","thermostat","heating-control","temperature-regulation"]
  questions: ["What does the Temperature hysteresis controller do?","When does the relay switch on and when does it switch off?","What hysteresis should I set?","How does the Temperature hysteresis controller control an analog valve?","Why does the temperature with a valve settle slightly below the setpoint?","When should I use the PID controller instead of the hysteresis controller?"]
---

# Temperature Hysteresis Controller

Last updated: 2026-11-11

**Temperature hysteresis controller** keeps the room temperature according to a thermostat: it
switches a switching output (boiler relay, thermal actuator, electric heating) on and off around the setpoint, and
opens an analog output (0–10 V valve) smoothly within the band. It is enough for ordinary room control — it has no
integral that would need tuning. This page describes the behavior from version 2026.1.

## Try the hysteresis controller



## Relay: switching on and off

In heating with the default **Plus** band, the relay switches on when the temperature drops to the
setpoint or below it, and switches off when the temperature exceeds the setpoint plus the hysteresis (0.2 °C by
default). In between, it leaves the relay as it is.

- **A larger hysteresis** means fewer switchings and a larger temperature swing; a smaller one the opposite. For a
  boiler and a thermal actuator, keep at least 0.2 °C; with a hysteresis of 0, the relay switches at every sensor change
  of a tenth of a degree.
- **The delay of the system** adds overshoot to the hysteresis: the relay switches off above the setpoint, but the
  radiator or the floor is still heating. Underfloor heating with a delay of half an hour overshoots by more than a
  degree (the **Floor on relay** scenario) — there, a valve in the band or the PID controller is a better choice.
- **Without a sensor value**, the controller crosses no threshold: the relay stays in its last state, even when it is
  on. A sensor outage is therefore guarded by the warning (item 5 of the settings).

## Valve: smoothly within the band

The hysteresis controller does not switch an analog output fully on, but sets it according to the position of the
temperature within the band: 100% at the lower edge of the band and below it, 0% at the upper edge and above it,
linearly in between. This is control by a P term with a proportional band equal to the width of the band. The band is
determined by the hysteresis and the mode:

| Band mode | Band at a setpoint of 21 °C and a hysteresis of 1 °C | Where the temperature settles |
|---|---|---|
| **Plus** | 21 to 22 °C | slightly above the setpoint |
| **Minus** | 20 to 21 °C | slightly below the setpoint |
| **Middle** | 20 to 22 °C | around the setpoint, exactly on it at half power |

The temperature settles where the valve gives exactly as much power as the room loses — in cold weather closer to the
lower edge, in warm weather closer to the upper edge. A narrower band reduces the deviation, but the valve then reacts
more sharply (the **Valve in band** scenario); with a hysteresis of 0, the valve always gives 50%. When you want no
deviation at all, use [**PID controller**](https://taphome.com/en/docs/smart-rules/pid-controller/):
its I term makes up the power the room needs permanently.

## Settings

1. **Thermostat** — the device with the measured and the set temperature; the controller
   evaluates it at every change.
2. **Heating & Cooling Mode** — a fixed mode, or from the season device.
3. **Hysteresis range** — **Range**
   and the band mode (**Plus**, **Minus**, **Middle**) separately
   for heating and cooling; cooling defaults to **Minus**. When the season offers both heating and
   cooling (a season device with both options, or the fixed heating and cooling mode), the cooling setpoint is shifted
   by "**Cooling set point offset in Heating and Cooling mode**".
4. **Output devices** — a digital output gets the switch-on and switch-off
   actions. In heating, the output can also watch the floor temperature
   ("**Floor temperature**"): above the maximum it switches off; an optional minimum
   (the room setpoint plus an offset, −1 °C by default) switches it on even when the room is warm. In cooling, the output
   switches off before the dew point ("**Dew point limit**") — this needs a coolant
   temperature sensor and humidity on the thermostat; without humidity, the protection is turned off.
5. **Enable warning when temperature range is exceeded** — a new rule has it on for 12–50 °C and sends it to
   the service group; it watches the thermostat as well as the floor and ceiling sensors.

## Hysteresis or PID controller

| | **Temperature hysteresis controller** | **PID controller** |
|---|---|---|
| Relay | switches on and off around the setpoint | through a TapHome Bus module output in **Pulse-width modulation** mode |
| Valve | smoothly within the band, settles slightly off the setpoint | smoothly, the I term brings it exactly to the setpoint |
| Settings | hysteresis and band mode | Kp, Ki, Kd, update rate, reset threshold |
| Floor protection and dew point | yes | no |

The PID controller makes sense when you need the setpoint
exactly — supply water behind a mixing valve, a fast system — or when a relay should switch smoothly through PWM
(section [Relay and PWM](https://taphome.com/en/docs/smart-rules/pid-controller/#pwm)).