Help needed: Multi-zone setup with OpenTherm Gateway and PWM thermostatic valves

[ndieschburg]

First of all, thank you for this amazing project! The work you've done on SAT is really impressive.

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My setup

• OpenTherm Gateway (OTGW) with TCP adapter controlling my boiler
• Multiple thermostatic valves (one per zone) that I want to control independently

What I tried

I've attempted several configurations without success. The most logical one to me (starting with a single valve to simplify) is:

1. One SAT instance with OpenTherm Gateway for my boiler, with the living room as the main room
2. One SAT instance in PWM mode (without multi-zone configuration) with my valve switch as the device

The problem

When I increase the temperature setpoint on the living room thermostat, I get the following error in the logs:

Logger: custom_components.sat.pwm
Source: custom_components/sat/pwm.py:87
PWM turned off due missing values.

This error occurs repeatedly (114 occurrences in about an hour).

My question

I really can't figure out how to properly configure multi-room support. What would be the recommended configuration for my use case (OpenTherm Gateway + multiple zone valves)?

Thank you in advance for your help!

[sergeantd83]

Better not use the On/Off ( PWM ) since it is not working properly at the moment. Set the OpenTherm option and then just add your climate entities ( TRVs ) in the rooms section.

[ndieschburg]

Thank you for your response. I'll try that. The problem is that my valves are not TRVs, but electric valves that I control with relay switches. I'll give it a try by creating a generic thermostat over the switches. Can you confirm that this is the right approach? Best regards.

[sergeantd83]

A simple generic thermostat with 0.1 cold and hot tolerance is enough. These generic thermostats will control the opening of every valve ( I assume that the valves are able to work on only in 2 positions OPEN and CLOSED )

[ndieschburg]

Hi,

I configured multi-zone as you suggested, using generic_thermostat for 2 additional zones with relay-controlled valves. This seems to work well for those zones.

However, I have a question regarding my main living room (salon): it doesn't have a valve and uses the boiler directly. I was planning to continue using the main SAT thermostat as I did before configuring multi-zone.

Since enabling multi-zone, I'm getting this warning:

2025-12-23 06:17:59.267 WARNING (MainThread) [custom_components.sat.climate] Cannot turn on heater: no valves are open

My understanding: Once multi-zone is enabled, the main SAT thermostat no longer controls the boiler directly, and I must create a zone even for rooms without valves?

My proposed workaround: Create a generic_thermostat with a dummy switch (that doesn't control anything physical) and add it to SAT's rooms configuration. This way, the "valve" would always appear as open when heating is requested.

Questions:

1. Is this the correct approach?
2. By doing this, am I losing any functionality from the main SAT thermostat (like the PID algorithm, climate curves, etc.)?

Thank you for your help!

[ndieschburg]

Update: Issue with multi-zone and primary thermostat

Hello, it's me again! Sorry to bother you, and thank you so much for your help on this project.

After more testing, I found a fundamental problem with the multi-zone setup: when no zone is requesting heat, the primary thermostat (my living room) cannot trigger heating on its own. SAT waits for zone demand, so the boiler stays off even if the primary room needs heat.

As a workaround, I added a dummy zone with a virtual valve that never opens. This forces SAT to see an active zone, but it also means I lose the PID/heating curve benefits on my primary room — it falls back to basic hysteresis control.

Proposed alternative approach

I'm considering abandoning SAT's built-in multi-zone feature and implementing my own zone election logic:

1. Create a single SAT thermostat with a virtual temperature sensor
2. On any room temperature change, calculate the delta (setpoint - current temp) for each zone
3. Elect the zone with the highest delta (most in need of heat)
4. Push that zone's temperature and setpoint to the virtual SAT thermostat

This way, SAT always regulates for the room that needs it most, preserving full PID/heating curve functionality, while I manage valve control separately via standard automations.

Would this approach make sense, or is there a better way to handle this use case within SAT?

Thanks again for your time and for this great project!

[sergeantd83]

Can you please add this dummy thermostat in the “Thermostat” section instead of the “Rooms” section and try again?

[ndieschburg]

Thank you so much for the quick response!
I was actually just going through the configuration options again (see screenshot below), and I'm still a bit confused about the difference between Thermostat, Primary, and Rooms.

I've read the documentation but it's not entirely clear in my mind how these three options interact with each other. Would you mind explaining it briefly?
In the meantime, I'll test your suggested solution and report back. Thanks again for your help!

[ndieschburg]

Still same messages :

2025-12-23 23:06:06.303 WARNING (MainThread) [custom_components.sat.climate] Cannot turn on heater: no valves are open.

[sergeantd83]

Is the state of this generic thermostat heat and hvac_action: heating? You can check it in the developer tools.

[ndieschburg]

Hi @Alexwijn and team! 👋

First of all, thank you so much for your amazing work on SAT. It's a fantastic integration and the PID algorithm works beautifully with my OpenTherm boiler. I really appreciate all the time and effort you've put into this project.

I wanted to follow up on my issue and share what I learned, in case it helps others.

The Problem

My boiler wasn't turning on even though SAT was calculating setpoints correctly. The flame never ignited because SAT thought no valves were open.

The Solution

After diving into the source code (specifically climate.py and config_flow.py), I finally understood what CONF_RADIATORS and CONF_ROOMS actually do:

Parameter	Role	SAT sends setpoint?	Used for valve detection
CONF_RADIATORS	Slave thermostats	Yes	Yes
CONF_ROOMS	Autonomous thermostats	No (keeps own setpoint)	Yes

Key insight: CONF_RADIATORS are not just "radiators to monitor" - they are slaves that SAT actively controls. SAT sends them the target temperature and checks their hvac_action to determine if valves are open (valves_open property in climate.py:519).

My mistake was leaving CONF_RADIATORS empty, thinking SAT would work standalone. Without any climate entities in RADIATORS or ROOMS, SAT had no way to know if any valve was open, so it never requested heat from the boiler.

My Setup Now

• CONF_RADIATORS: climate.thermostat_salon_control (generic_thermostat controlling my main zone electrovalve)
• CONF_ROOMS: climate.chauffage_unai, climate.chauffage_naia (bedroom thermostats with their own setpoints)
• SDB thermostat: Used as a bypass valve (safety feature when all main valves close while flame is on)

Everything works perfectly now! 🎉

Suggestion

Maybe the documentation or config flow could clarify that:

1. At least one climate entity should be in RADIATORS or ROOMS for SAT to detect open valves
2. RADIATORS are "slaves" that receive SAT's setpoint, while ROOMS keep their own setpoint

Thanks again for this great integration. Happy holidays! 🎄

[Alexwijn]

Thanks! Please update to the latest release and report back it this resolves it.

[github-actions]

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