Set max modulation

The Set max modulation action overrides the maximum relative modulation level on your OpenTherm Gateway. Normally, the thermostat controls the maximum modulation level on the boiler. Setting this to any value other than -1 enables the override and lets the OpenTherm Gateway control this setting. Because of the potential consequences of leaving this setting enabled, the override is disabled when Home Assistant shuts down or restarts.

You only need this if you are writing your own software thermostat.

Using this action from the user interface

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

To set the maximum modulation from an automation or a script:

1. Go to Settings > Automations & scenes.
2. Open an existing automation or script, or select Create automation > Create new automation.
3. If you’re setting up a new automation, add a trigger in the When section. Scripts don’t need a trigger. They run when something else calls them.
4. In the Then do section, select Add action.
5. From the search box, search for and select OpenTherm Gateway: Set max modulation.
6. Enter the Gateway ID and the Level.
7. Select Save.

This action does not support targets. In the UI, you are not prompted to choose an area, device, entity, or label.

Options in the UI

Using this action 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, refer to this action as opentherm_gw.set_max_modulation. A basic example looks like this:

action: opentherm_gw.set_max_modulation
data:
  gateway_id: opentherm_gateway
  level: 50

This limits the maximum modulation level to 50% on the selected gateway.

Options in YAML

Try it yourself

Ready to test this? Open Developer tools > Actions, search for this action, fill in the fields, and select Perform action. You see what happens 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] without writing a line of YAML.

More examples

Real scenarios where this action shows up in automations and scripts. Copy any example and adapt it to your setup.

Still stuck?

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

Related actions

These actions work well alongside this one:

• Set control setpoint: Sets the central heating control setpoint override on the gateway.

• Set central heating override: Sets the central heating override option on the gateway.