Water heater turned on

The Water heater turned on trigger fires when a water heater entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] changes from off to on. It does not depend on which operation mode the water heater uses after turning on. Use it when you want to react as soon as hot water heating becomes active again, like starting a recirculation pump or restoring a normal schedule.

When you target more than one water heater, the Trigger when option controls whether the automation runs for each water heater that turns on, only for the first one, or only after all targeted water heaters are on.

Using this trigger from the user interface

If you prefer building automations visually, Home Assistant walks you through this trigger step by step. You pick what to watch, tweak a few options, and save. No YAML knowledge required.

To use Water heater turned on in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the When section, select Add trigger.
4. Select what you want to monitor. Under By target (see Targets), pick the area your water heater is in, or select a device, a specific entity, a floor, or a label.
5. From the triggers shown for that target, select Water heater turned on.
6. Under Trigger when (see Behavior), pick Each, First, or All.
7. Under For at least, enter how long the water heater must stay on before the trigger fires.
8. Select Save.

Options in the UI

Using this trigger in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required.

In YAML, Water heater turned on is referred to as water_heater.turned_on. A basic example looks like this:

trigger: water_heater.turned_on
target:
  entity_id: water_heater.utility_room

This fires when water_heater.utility_room turns on.

To wait until all targeted water heaters are on:

trigger: water_heater.turned_on
target:
  label_id: basement_water_heaters
options:
  behavior: last
  for: "00:05:00"

Options in YAML

YAML sometimes provides additional options for more complex use cases that are not available through the UI.

Targets of the trigger

This trigger requires a target. The target is the object that Home Assistant will watch. You can select a single entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], a device, an area, a floor, or a label as a target, and Home Assistant will watch every matching water_heater entity behind that target.

• Entity: one specific water_heater entity, such as water_heater.living_room.
• Device: every water_heater entity that belongs to a device.
• Area: every water_heater entity in a room or area.
• Floor: every water_heater entity on a floor.
• Label: every water_heater entity that shares a label.

You can also select different target types in one trigger. For example, you can add a specific entity and an area as targets in the same trigger to monitor both of them at once.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Trigger when option controls how the trigger responds:

• Each (any in YAML, default): the trigger fires every time any one of the targeted entities transitions. For example, if you monitor three motion sensors in the living room and someone walks past sensor 1, the automation fires. When they walk past sensor 2 a moment later, it fires again. Every individual event counts.
• First (first in YAML): the trigger fires only on the first transition in the targeted group, then waits until all targeted entities have reset before it fires again. For example, if you monitor the same three motion sensors, the automation fires when the first one picks up movement (someone entered the room). The other two firing afterward are ignored, so you get one notification per “someone walked in” event instead of three.
• All (last in YAML): the trigger fires only after the last targeted entity in the group has fired, meaning all of them are now in the expected state. For example, if you monitor the lights in the living room, bedroom, and hallway, the automation fires only once all three have turned off. This is useful for scenarios like “start the robot vacuum only after every light on the floor is off,” so you know the room is truly empty.

Good to know

• This trigger fires when the water heater changes from off to on, regardless of whether it comes back in eco, electric, heat_pump, or another supported mode.
• Use Water heater operation mode changed if you need to react only to a specific operating mode.
• unavailable and unknown do not count as on for this trigger.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, then change the state of the targeted entity to watch the trigger fire on your actual entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup.

Automation: start recirculation when the water heater turns on

When the water heater turns on, start the recirculation pump so hot water is available sooner at nearby fixtures.

• Trigger: Water heater turned on
  • Target: Utility room water heater
• Action: Turn on switch

alias: "Start recirculation when the water heater turns on"
triggers:
  - trigger: water_heater.turned_on
    target:
      entity_id: water_heater.utility_room
actions:
  - action: switch.turn_on
    target:
      entity_id: switch.hot_water_recirculation

Automation: restore the normal operating mode when all basement water heaters come back on

When all targeted water heaters are back on for 5 minutes, switch them to your normal operating mode.

• Trigger: Water heater turned on
  • Target: Basement water heaters
  • Trigger when: All
  • For at least: 00:05:00
• Action: Set water heater operation mode

alias: "Restore water heater mode after startup"
triggers:
  - trigger: water_heater.turned_on
    target:
      label_id: basement_water_heaters
    options:
      behavior: last
      for: "00:05:00"
actions:
  - action: water_heater.set_operation_mode
    target:
      label_id: basement_water_heaters
    data:
      operation_mode: heat_pump

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the trigger you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related triggers

These triggers work well alongside this one:

• Water heater turned off: Triggers after one or more water heaters turn off.

• Water heater operation mode changed: Triggers after the operation mode of one or more water heaters changes to a specific mode.