Viessmann Boiler Fault Codes Explained

How do I read a Viessmann fault code?

Look at the code as well as the fault symbol. On the Vitodens 100-W WB1B every fault flashes, and the code tells you the type: F codes such as F2 and F4 lock the burner out until it is reset, while sensor faults clear themselves once the cause is fixed, so pressing reset does nothing. Newer touch-display models show R next to the flashing symbol when the burner is locked out.

The codes fall into rough groups. Two-digit numbers such as 10, 18, 30 and 38 are sensor faults, a short circuit or a broken lead on the outside, boiler water or return sensor. Codes starting with F, such as F2, F4 and F9, mean the burner control unit is in a fault state. A9 and similar codes are communication faults with a connected thermostat or control.

Viessmann builds several generations of Vitodens, and its own online fault checker lists some codes against specific models only. The table in your boiler’s manual is the final word for your model.

Which Viessmann codes come up most often?

These are the lockouts householders most often search for, with what Viessmann’s own documentation says about each.

• F2, temperature limiter has responded: the boiler overheated. Viessmann’s checks start with the system water level, the circulation pump and venting air from the system.
• F4, no flame signal: the boiler tried to light and did not see a flame. The manual lists the ignition and ionisation electrode, gas pressure, the gas valve, the ignition module and the condensate drain.
• F1: maximum flue gas temperature exceeded on the Vitodens 100-W WB1B, with the same water and pump checks as F2.
• F9 and FA: fan faults, either the fan speed is too low at start-up or the fan has not stopped when it should.

Only a pressure top-up and a single reset are householder jobs. Everything else in the list involves testing inside the casing. If you smell gas, ventilate, shut the meter valve if you can reach it safely, leave switches alone, and call 0800 111 999 from outside before anything else.

What can I safely try on a Viessmann?

Check the pressure gauge. Low water is behind many overheat trips, and if it is low our boiler pressure repair page covers what to do. Check other gas appliances work and a prepayment meter has credit. In freezing weather, look at the condensate pipe outside, because Viessmann lists the condensate drain as an F4 cause.

Then reset once, only for an F code, or when R shows next to the flashing fault symbol on newer models. On older Vitodens models with rotary selectors you turn the selector briefly to the reset position and back. On other models, follow the reset step in your user manual. If the same code returns, stop.

Getting a Viessmann repaired

Gas work is carried out by Gas Safe registered engineers. The engineer reads the fault history, tests the part the code points to and tells you what they find. The visit starts with the £60 call-out and the repair price is agreed with you on site before any work starts. Book through boiler repairs, or emergency boiler repair if you have no heat or hot water tonight.