How to "Replace" an Exacontrol E7 C Thermostat and Control Your Boiler with Home Assistant

[axelere]

How to "Replace" an Exacontrol E7 C Thermostat with Home Assistant for Boiler Control

This post is here to help anyone like me who isn’t familiar with eBUS avoid wasting hours heading in the wrong direction.

Context

I have a Saunier Duval ThemaFast Condens 30 boiler for hot water and underfloor heating, originally controlled by the Exacontrol E7 C thermostat with an outdoor temperature sensor.

I’m using an eBUS Adapter Shield C6 (Wi-Fi version) to connect the boiler to Home Assistant via the eBUS protocol.

Goal

Initially, I wanted to completely replace the Exacontrol E7 C thermostat (which I find unattractive) with a wall-mounted tablet running a Home Assistant dashboard. That dashboard would then act as the thermostat and control the boiler.

Problem

I quickly realized this wasn’t possible because the heating curve is stored in the thermostat, not in the boiler. Removing the thermostat would mean losing heating logic altogether.

---

Final Setup

I moved the E7 C thermostat to the boiler room and decided to override its temperature reading dynamically using data from a reference room (like the living room).

That way, the thermostat thinks it's in the reference room, even though it's physically somewhere else.

---

Requirements

1. Properly configure your eBUS adapter
2. Follow this guide:
   HOW TO: Write values from Home Assistant controls to ebusd (Idiot's guide)

---

MQTT Entity Setup

If everything is working, your devices will begin to show up one by one in MQTT (this might take a few minutes).

Make sure the thermostat exposes these three values:

• RoomTemp temp → Measured room temperature
• RoomTempCorr → Correction value to be applied
• RoomTempCorrFact → Factory correction value

---

Allow Writing to RoomTempCorr

In the ebusd CSV definitions, RoomTempCorr is marked as wi (write install), meaning it can only be changed in installer mode.

To bypass this restriction, add this to your Custom Command Line Options in the Home Assistant ebusd add-on:
--accesslevel=*

Save and restart the add-on.

---

Testing via Developer Tools

Go to Developer Tools > Services in Home Assistant, and run:

service: mqtt.publish
data:
  topic: "ebusd/e7c/RoomTempCorr/set"
  payload: -20
  evaluate_payload: false

Example: This will raise the thermostat’s displayed temperature by -20°C.
So if your room is actually 25°C, it should now display 5°C — and if your setpoint is 20°C, the boiler will turn on since the virtual temperature is below it.

---

Dynamic Thermostat Correction via Node-RED & eBUS

This setup allows you to dynamically adjust your boiler thermostat's reading so it behaves as if it were located in another room — without physically moving it.

Formula

To automate this, apply this basic formula:

RoomTempCorr = ReferenceRoomTemp - (RoomTempTemp + RoomTempCorrFact)

This way, the thermostat can think it's in the reference room (living room, bedroom, etc.) rather than the boiler room.

I mainly use Node-RED so here is the code:

Click to expand Node-RED flow JSON

[{"id":"1712581bcc894201","type":"trigger-state","z":"ede4cf8a90bd86c4","name":"Temperatures","server":"808d0070.6617c","version":5,"inputs":0,"outputs":2,"exposeAsEntityConfig":"","entities":{"entity":["sensor.ebusd_e7c_roomtemp_temp","sensor.controleur_fan_rack_temperature_entree_rack"],"substring":[],"regex":[]},"debugEnabled":false,"constraints":[],"customOutputs":[],"outputInitially":true,"stateType":"str","enableInput":false,"x":250,"y":1380,"wires":[["492a95945b9f884b","8fdb5de0eb18e72a","5c479c40c19455ee"],[]]},{"id":"492a95945b9f884b","type":"api-current-state","z":"ede4cf8a90bd86c4","name":"","server":"808d0070.6617c","version":3,"outputs":1,"halt_if":"","halt_if_type":"str","halt_if_compare":"is","entity_id":"sensor.ebusd_e7c_roomtemp_temp","state_type":"str","blockInputOverrides":true,"outputProperties":[{"property":"payload","propertyType":"msg","value":"","valueType":"entityState"},{"property":"data","propertyType":"msg","value":"","valueType":"entity"}],"for":"0","forType":"num","forUnits":"minutes","override_topic":false,"state_location":"payload","override_payload":"msg","entity_location":"data","override_data":"msg","x":550,"y":1380,"wires":[["a70eecc141401f58"]]},{"id":"8fdb5de0eb18e72a","type":"api-current-state","z":"ede4cf8a90bd86c4","name":"","server":"808d0070.6617c","version":3,"outputs":1,"halt_if":"","halt_if_type":"str","halt_if_compare":"is","entity_id":"sensor.ebusd_broadcast_outsidetemp","state_type":"str","blockInputOverrides":true,"outputProperties":[{"property":"payload","propertyType":"msg","value":"","valueType":"entityState"},{"property":"data","propertyType":"msg","value":"","valueType":"entity"}],"for":"0","forType":"num","forUnits":"minutes","override_topic":false,"state_location":"payload","override_payload":"msg","entity_location":"data","override_data":"msg","x":560,"y":1420,"wires":[["a70eecc141401f58"]]},{"id":"a70eecc141401f58","type":"join","z":"ede4cf8a90bd86c4","name":"","mode":"custom","build":"array","property":"","propertyType":"full","key":"topic","joiner":"\\n","joinerType":"str","useparts":false,"accumulate":false,"timeout":"","count":"3","reduceRight":false,"reduceExp":"","reduceInit":"","reduceInitType":"","reduceFixup":"","x":860,"y":1380,"wires":[["e87542481188255a"]]},{"id":"e87542481188255a","type":"function","z":"ede4cf8a90bd86c4","name":"Calc diff","func":"let sejour = null;\nlet chaudiere = null;\nlet correction = 0;\n\nfor (let i = 0; i < msg.payload.length; i++) {\n const entity = msg.payload[i].data.entity_id;\n const value = parseFloat(msg.payload[i].data.state);\n\n if (entity.includes(\"sensor.ebusd_broadcast_outsidetemp\")) {\n sejour = value;\n } else if (entity.includes(\"roomtemp_temp\")) {\n chaudiere = value;\n } else if (entity.includes(\"roomtempcorrfact\")) {\n correction = value;\n }\n}\n\n// Vérification des valeurs valides\nif (sejour === null || chaudiere === null) {\n node.error(\"Données manquantes pour le calcul.\");\n return null;\n}\n\n// Calcul\nlet result = sejour - (chaudiere + correction);\n\n// Arrondi à 2 décimales\nmsg.payload = parseFloat(result.toFixed(2));\n\nreturn msg;\n","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":1000,"y":1380,"wires":[["5c801c7f3ea0797f"]]},{"id":"5c801c7f3ea0797f","type":"mqtt out","z":"ede4cf8a90bd86c4","name":"","topic":"ebusd/e7c/RoomTempCorr/set","qos":"","retain":"","respTopic":"","contentType":"","userProps":"","correl":"","expiry":"","broker":"","x":1210,"y":1380,"wires":[]},{"id":"5c479c40c19455ee","type":"api-current-state","z":"ede4cf8a90bd86c4","name":"","server":"808d0070.6617c","version":3,"outputs":1,"halt_if":"","halt_if_type":"str","halt_if_compare":"is","entity_id":"sensor.ebusd_e7c_roomtempcorrfact","state_type":"str","blockInputOverrides":true,"outputProperties":[{"property":"payload","propertyType":"msg","value":"","valueType":"entityState"},{"property":"data","propertyType":"msg","value":"","valueType":"entity"}],"for":"0","forType":"num","forUnits":"minutes","override_topic":false,"state_location":"payload","override_payload":"msg","entity_location":"data","override_data":"msg","x":550,"y":1340,"wires":[["a70eecc141401f58"]]},{"id":"808d0070.6617c","type":"server","name":"Home Assistant","addon":true,"rejectUnauthorizedCerts":true,"ha_boolean":"","connectionDelay":false,"cacheJson":false,"heartbeat":false,"heartbeatInterval":"","statusSeparator":"","enableGlobalContextStore":false}]

Node function code:

let sejour = null;
let chaudiere = null;
let correction = 0;

for (let i = 0; i < msg.payload.length; i++) {
    const entity = msg.payload[i].data.entity_id;
    const value = parseFloat(msg.payload[i].data.state);

    if (entity.includes("sensor.ebusd_broadcast_outsidetemp")) {
        sejour = value;
    } else if (entity.includes("roomtemp_temp")) {
        chaudiere = value;
    } else if (entity.includes("roomtempcorrfact")) {
        correction = value;
    }
}

if (sejour === null || chaudiere === null) {
    node.error("Missing data for temperature calculation.");
    return null;
}

let result = sejour - (chaudiere + correction);
msg.payload = parseFloat(result.toFixed(2));

return msg;

---

Results

Since I haven't moved thermostat to boiler room yet, I used outside temperature as reference temperature. Here are the results:
Thermostat sensor temperature:

Outdoor sensor temperature:

Difference between thermostat and outdoor sensor:

Thermostat display temperature:

• Thermostat's displayed temperature is successfully overridden
• Heating behaves as if it were based on the chosen reference room
• Control is now fully handled via Home Assistant

---

Example Use Cases

• The thermostat is in a room that is unusually warm or cold
• You want the heating to be regulated based on a different room’s temperature
• You can switch reference rooms based on time of day:
  • 6h to 18h → living room
  • 18h to 6h → bedroom

---

Final Thoughts

This method allows you to modernize your heating system while keeping the internal logic of the original thermostat (especially the heating curve).
You don’t need to reverse-engineer or replace everything — just redirect the key sensor input.
There you go, I hope this helps 😊

Axel