Bosch Thermotechnology · Error codes
Bosch/Buderus GB312 3C 538 — Fan Speed Too Slow.
3C 538
Fan speed too slow. The actual speed detected is slower than the set speed. Checks: Dirt in fan. Fan defective. Remedy: Clean fan if necessary. Replace fan. The table classifies it as V (interlocking).
Applies to
This venting or air-supply 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 venting or air-supply code points at the combustion-air path: a blocked terminal, a restricted flue, a failed fan, or a condensate restriction. It does not say which, and running an appliance with a blocked flue is unsafe.
Safe things to observe
- If a carbon-monoxide alarm sounds anywhere in the building, leave immediately and call 911 from outside.
- From a safe distance, check that the vent terminal and combustion-air inlet are not blocked.
- Do not run the appliance while a blockage is suspected.
Do not
- Do not put anything into the vent or air-intake openings.
- Do not remove or modify vent pipe.
How professional service helps
- A technician inspects the full vent and combustion-air path, clears blockages and checks the fan.
- 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.
Parts and service
Parts commonly involved
These parts appear in the documented text for this alert. A code reports a condition, not a failed part — a technician confirms the cause by testing before anything is replaced.
Combustion fan (blower)
The combustion fan is the sealed boiler's lungs: it draws in combustion air, keeps the burner's gas-air mixture correct, and pushes flue gases out…
What a technician checks →
Service for this alert
- Gas Boiler Repair
Licensed gas technicians from ROMA Heating & Cooling diagnose and repair residential and light-commercial gas boilers across…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Bosch Thermotechnology Buderus GB312 (Logano plus GB312).
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.