Bosch Thermotechnology · Error codes
Bosch/Buderus GB312 5L 543 — No Communication with Safe.
5L 543
No communication with SAFe. The MC10 is not receiving any data from the SAFe. Checks: Check whether the plugs on the cables (bus connecting cable and power cable) between the SAFe and the MC10 are properly connected. On the MC10, check whether 120 V is present at the "Power SAFe" terminals. Check whether the connecting cables (bus cable and power cable) between the SAFe and the MC10 are damaged. Check whether the green indicator lamp on the SAFe is lit. Disconnect the bus cable and check whether the boiler goes into emergency mode (runs up to boiler temperature of approx. 140 °F (60 °C)). Check whether the SAFe or the MC10 is defective by replacing them. Remedy: If connector is loose, reconnect properly. If 120 V is not present, the MC10 is defective and must be replaced. Replace connecting cable. If the LED is not lit, the SAFe is probably defective and should be replaced. If the boiler does not start up, the SAFe is defective and must be replaced. Replace the SAFe or MC10. The table classifies it as K.
Applies to
This communication or network fault code is displayed by the Logamatic BC10 basic control unit and MC10 control unit (SAFe fault codes) on Logano plus GB312 models (90–280), as documented in Buderus Logano plus GB312 Installation and Service Instructions, doc 6 720 806 273 (01.2013), section 10.2.2 Table 23 Fault displays (6 720 806 273). Codes can differ between controller generations, so always check the manual that matches your unit.
- Bosch Thermotechnology Buderus GB312 (Logano plus GB312)
- Buderus GB312/90
- Buderus GB312/120
- Buderus GB312/160
- Buderus GB312/200
- Buderus GB312/240
- Buderus GB312/280
Controller: Logamatic BC10 basic control unit and MC10 control unit (SAFe fault codes). Source manual: 6 720 806 273 (2013-01).
Why a code is not a diagnosis
A communication code involves the link between controls (cascade, remote, sensors on a bus). Another unit being off, a wiring fault or an address conflict can all produce it.
Safe things to observe
- Check that every appliance in a multi-unit plant has power.
- Report the code together with any other codes on the system.
Do not
- Do not re-address or rewire control networks yourself.
How professional service helps
- A technician verifies power, wiring and settings across the connected units.
- Combustion and safety devices are verified with an analyser and the manufacturer's procedure after any repair.
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Frequently asked questions
Can I clear this code myself?
Clearing a code without fixing its cause usually just brings it back. Note the code, check the safe items on this page, then call a licensed technician. If your appliance manual describes a user reset for this exact code and it stays away, no call may be needed.
Boiler locked out? Call with the alert text ready.
The brand, model and this alert are passed along when you request service online, so the technician arrives prepared.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- Buderus Logano plus GB312 Installation and Service Instructions, doc 6 720 806 273 (01.2013), section 10.2.2 Table 23 Fault displays · 6 720 806 273 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.