By AJ, certified Gas Safe engineer and lead plumber at 247 Emergency Plumbers Edinburgh · Codes checked
A Viessmann fault code tells you why the boiler has stopped or locked out. Some, such as low pressure or a frozen condensate pipe, you can safely check yourself; most others need a Gas Safe registered engineer. Find your code below. These are Viessmann's published codes for Vitodens 200-W and 300-W boilers with Vitotronic controls. Viessmann notes that codes on newer models may differ, and strongly advises homeowners not to carry out repairs themselves or open the appliance.
Smell gas, or a carbon monoxide alarm is sounding? Do not reset the boiler. Open windows, turn off the gas at the meter if it is safe to do so, leave the building and call the free gas emergency line on 0800 111 999. What to do →
Viessmann fault codes and what to do
F2Engineer needed
What it means: The boiler temperature limiter has tripped (overheat).
What to do: Check the pressure gauge. Do not keep resetting; call a heating engineer.
A4Engineer needed
What it means: Maximum system pressure exceeded.
What to do: Do not top up. Call a heating engineer.
F1Engineer needed
What it means: Flue gas temperature has exceeded its limit.
What to do: Switch off and call a Gas Safe engineer.
F8Engineer needed
What it means: The fuel (gas) valve closes late.
What to do: Switch off and call a Gas Safe engineer.
E5Engineer needed
What it means: Flame amplifier fault; the burner is blocked.
What to do: Needs a Gas Safe engineer.
30 / 38Engineer needed
What it means: Boiler temperature sensor short circuit (30) or open circuit (38); the burner is blocked.
What to do: Needs an engineer.
50Engineer needed
What it means: Cylinder temperature sensor short circuit: no hot water.
What to do: Heating may still work. Call an engineer.
10 / 18You may be able to fix this
What it means: Outdoor temperature sensor fault; the control runs as if it is 0°C outside.
What to do: The heating keeps working, so this can usually wait for a planned visit.
A7Engineer needed
What it means: Control panel defective.
What to do: Needs an engineer.
b5 / F0 / FFEngineer needed
What it means: Internal control fault (FF can also mean the reset button is stuck).
What to do: Needs an engineer.
Safe checks you can do for most codes
These are the only checks we suggest without an engineer. Never remove the boiler casing.
Pressure: look at the gauge. Most boilers need about 1 to 1.5 bar when cold. If it is low, top up using the filling loop as shown in your manual.
Gas supply: check your cooker or hob works, and that a prepayment meter has credit.
Frozen condensate pipe: in freezing weather, warm the white plastic pipe outside with warm (not boiling) water or a hot-water bottle, only where you can reach it from the ground. How to thaw it safely →
One reset: press reset once, as your manual describes. If the code comes back, stop and call an engineer; repeated resets can lock the boiler out.
Controls: check the programmer, thermostat and any smart controls are calling for heat.
Code still showing? Our Gas Safe engineers can fix it.
Boiler repair labour is £90–£350 in standard hours, plus the callout from £75 (out of hours £100–£180). The price is agreed before work starts. Tell us the make, model and code when you call.
Our emergency line is open 24 hours a day, 7 days a week.
Fault codes vary by model and software version. Always check your boiler’s own manual. This page is general guidance, not a diagnosis.
YOUR QUESTIONS, ANSWERED
Helpful answers before you call.
What does Viessmann F2 mean?
The boiler temperature limiter has tripped (overheat). Check the pressure gauge. Do not keep resetting; call a heating engineer.
What does Viessmann A4 mean?
Maximum system pressure exceeded. Do not top up. Call a heating engineer.
What does Viessmann F1 mean?
Flue gas temperature has exceeded its limit. Switch off and call a Gas Safe engineer.
What does Viessmann F8 mean?
The fuel (gas) valve closes late. Switch off and call a Gas Safe engineer.
Can I fix a Viessmann fault code myself?
Only simple checks: topping up low pressure, checking the gas supply and meter credit, thawing a frozen condensate pipe and one reset. Codes such as 10 / 18 can sometimes be cleared this way. Anything involving the gas valve, fan, flue or sensors needs a Gas Safe registered engineer.
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