E06 error and thermostat cannot detect external boiler or heat pump communication bus.

Safety first: Turn off power to both the thermostat and the boiler/heat pump before touching bus wiring.

• Step 1 – Verify compatibility: Confirm that the Atlantic thermostat model supports the same protocol as the boiler (e.g. OpenTherm). If the boiler is on/off only, disable bus mode in the installer menu and use relay contacts instead.
• Step 2 – Check wiring polarity: At the thermostat backplate, verify that the two bus terminals (e.g. OT+ and OT−) are correctly wired to the corresponding boiler terminals. Reverse the pair if the manual indicates polarity sensitivity.
• Step 3 – Inspect cable: Follow the bus cable route and look for damage, kinks, or junction boxes where connections may be loose. Tighten all terminal screws.
• Step 4 – Bus isolation test: Disconnect the bus wires at the thermostat and boiler. Use a multimeter to check for shorts between the two conductors or to earth. Repair or replace damaged cable if a short is found.
• Step 5 – Reset boiler and thermostat: Power up the boiler first, wait until it is fully initialized, then power up the thermostat. Some systems require this sequence for proper bus negotiation.
• Step 6 – Replace thermostat or interface: If E06 persists with known‑good wiring and a compatible boiler, the communication transceiver on the thermostat main PCB may be defective. Replace the thermostat or, if used, the separate Atlantic bus interface module.