Is your boiler showing a code starting with F and refusing to start? That code is a precise message: it tells the technician where to look. Here are the most common codes on Vaillant boilers (ecoTEC, turboTEC), which are very close to those of Bulex and Saunier Duval boilers, brands of the same group.
F22: lack of water, pressure too low
The most common code, and the only one you can often solve yourself. The heating circuit pressure has dropped too low. Top up to about 1.5 bar following our guide to low boiler pressure. If the code keeps coming back, there is a leak or a faulty expansion vessel.
F28: ignition failure
The boiler tried to ignite several times without detecting a flame. Possible causes:
- gas tap closed, prepayment meter empty or gas supply interrupted;
- condensate drain frozen or blocked (common in severe cold);
- worn or dirty ignition electrodes;
- faulty gas valve or circuit board.
Check the gas supply, then try one single reset. If the fault returns, a repair is needed.
F29: flame lost during operation
The boiler ignited, then the flame went out. The causes are the same as for F28, plus a possible problem with the flue or the air supply (blocked duct, strong wind). One reset, then a technician if the fault persists.
F75: no pressure change when the pump starts
On start-up, the boiler checks that the pump raises the pressure. If it detects nothing, it shows F75. The usual causes are a dirty pressure sensor, a tired pump or air in the circuit. Bleeding the radiators and checking the pressure may be enough; otherwise a technician must replace the sensor or the pump.
Other brands: Viessmann, Remeha, Junkers, Bosch…
Each manufacturer has its own code system. The principle is the same: note the code, check the manual and do not reset the boiler over and over. Our technicians repair all brands.
What not to do
- Resetting ten times in a row: you may make the fault worse.
- Opening the casing or removing a part: the gas circuit is reserved for approved professionals.
- Ignoring a code that keeps returning: it is the sign of a part reaching the end of its life.
Frequently asked questions
What does F22 mean on a Vaillant boiler?
F22 means lack of water: the heating circuit pressure is too low. Top up to about 1.5 bar.
What does F28 mean on a Vaillant or Bulex boiler?
F28 indicates an ignition failure: the boiler detects no flame. Check the gas supply, try one reset, then call a technician.
What should I do when the boiler shows F75?
Check the pressure and bleed the radiators. If the code returns, the pressure sensor or the pump must be checked by a technician.