Viessmann Vitocrossal 300 F8 — Burner in Fault Mode
F8
Burner in fault mode. The gas valve closes too late, so the burner is in fault mode; check the gas valve and both control wiring connections, and press reset button R. The table classifies it as Burner in fault mode.
If you smell gas
- Stop what you are doing. Do not use phones, switches, matches or anything that can spark inside.
- Go outside and leave the door open behind you.
- Call the FortisBC 24-hour emergency line at 1-800-663-9911 or dial 911.
Only after that, call ROMA about the boiler. Official guidance: FortisBC gas leaks and odour.
Applies to
This gas-train fault code is displayed by the Vitotronic 200 control (CU3A) on Vitocrossal 300 CU3A models (CU3A-94, CU3A-125, CU3A-160, CU3A-199), as documented in Vitocrossal 300 CU3A Service Instructions, doc 5673 649 - 20, 03/2025 (5673 649 - 20). Codes can differ between controller generations, so always check the manual that matches your unit.
- Viessmann Vitocrossal 300 (CU3A)
- Viessmann Vitocrossal 300 CU3A-94
- Viessmann Vitocrossal 300 CU3A-125
- Viessmann Vitocrossal 300 CU3A-160
- Viessmann Vitocrossal 300 CU3A-199
Controller: Vitotronic 200 control (CU3A). Source manual: 5673 649 - 20 (2025-03).
Why a code is not a diagnosis
A gas-train code involves the gas valve or its electrical circuit. It does not mean there is a leak; the circuit, coils and wiring must be measured by a licensed technician.
Safe things to observe
- If you smell gas, stop, go outside and call your gas utility's emergency line or 911 before anything else.
- Note the exact code and what the appliance was doing when it appeared.
- Check whether other gas appliances in the building are working.
Do not
- Do not reset or run the appliance while the gas valve circuit is suspect.
- Do not touch the gas valve.
How professional service helps
- A technician verifies harness connections and coil resistances against the manual before replacing parts.
- 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.
Gas valve
The gas valve is the boiler's controlled gateway for gas: it opens only when the control has proven safe conditions, meters the fuel to the burner,…
What a technician checks →Burner assembly
The burner assembly is where gas and air meet and burn inside a boiler, and its condition decides whether combustion is clean or makes carbon…
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 Viessmann Vitocrossal 300 (CU3A).
Frequently asked questions
Does this code mean I have a gas leak?
Not by itself. If you smell gas, stop, leave the building and call your gas utility's emergency line or 911 from outside before anything else. Otherwise the code points to a fault a technician confirms on site.
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
- Vitocrossal 300 CU3A Service Instructions, doc 5673 649 - 20, 03/2025 · 5673 649 - 20 · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.