Can I reset my Viessmann boiler to clear the F9 code?

You can reset once if your manual says it's safe. If the code returns, stop resetting — repeated resets on a genuine fault, especially gas or overheat faults, can be unsafe and may worsen the problem. Book a licensed repair instead.

Is the F9 fault dangerous?

Treat it as urgent. This code involves systems where continued operation can be unsafe. Turn the boiler off if it keeps recurring and call for a licensed repair; if you smell gas, leave and call your gas utility's emergency line.

How much does it cost to fix a Viessmann F9 fault?

Cost depends on the underlying cause — some causes (like low pressure or a dirty sensor) are minor, while others (like a gas valve or control board) cost more. We diagnose first and give you a clear price before any repair.

Viessmann Error Code

Viessmann Error Code F9

Fan speed too low at start.

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If your Viessmann combi boiler is showing error code F9, here's what it means: Fan speed too low at start. This is an urgent fault. Stop using the boiler if it keeps recurring and book a licensed repair promptly — especially if it involves gas, ignition, overheating or the flue.

Viessmann boilers report faults using f-series and e-series codes (e.g. f2, ea). Knowing the code helps a technician arrive prepared with the right parts, which usually means a faster, lower-cost repair.

What causes the F9 code?

Error F9 on a Viessmann boiler is most commonly caused by one of the following:

Fan bearing wear
Obstruction
Fan control fault

What you can safely check first

Note the exact code and your boiler's model number
Check the pressure gauge — low pressure triggers many faults
Confirm the gas supply is on and other gas appliances work
Reset the boiler once, per the manual, only if it's safe to do so
If the code returns, stop and call a licensed technician

Why this needs a licensed technician

Resolving a F9 fault almost always involves the gas, combustion, sensor or pressurized side of the appliance. Under BC's Safety Standards Act, that work must be performed by a licensed gas fitter — and doing it correctly protects your warranty and your safety. We diagnose Viessmann boilers, carry common parts, and verify clean combustion before returning your boiler to service.

Smell gas or suspect carbon monoxide? Leave now.

If you smell gas, hear hissing, or your CO alarm sounds, leave the building immediately and call your gas utility's emergency line from outside. Do not operate switches or relight the appliance. Once you are safe, call us for a licensed repair.

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Frequently Asked Questions

Other Viessmann codes & help

Viessmann F2Burner lockout — temperature limiter has tripped.Viessmann F4No flame established at start-up.Viessmann F5Fan / air pressure fault.Viessmann F6Auxiliary / flue gas temperature sensor fault.Viessmann FABurner blower does not stop / fan fault.All Viessmann Error CodesFull list

Fix Your Viessmann F9 Fault

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