Viessmann A2 Fault

Viessmann A2 Fault

When the Viessmann A2 fault code appears, it usually indicates that there is something wrong with the flue gas or exhaust system. Such an error can happen when the boiler registers inappropriate temperature of the flue gases implying that there is a problem with exhaust system. There are several causes of this fault condition such as blocked flues, improper installation and faulty sensors for flue gas. The understanding of what has caused them and necessary steps to take in order to resolve these issues should be known for boilers’ safe operation.

Flue Gas Sensor Fault: The A2 fault code could be due to a defective or misaligned flue gas sensor which produces incorrect readings.

Blockage in the Flue System: Various objects like nests from birds, debris, too much soot and other may block exhaust gases leading to failure registration by a boiler.

Improper Flue Installation: If an incorrectly installed flue does not vent out exhaust gases properly, abnormal temperatures will occur causing an A2 error.

Condensate Blockage:  This may affect condensing boilers whereby blocking of their condensate pipes results into poor disposal conditions for condensation hence affecting its temperature in flues.


Inspect the Flue Gas Sensor: It is necessary to examine whether there exist visible damages or misplacement of such kind of sensors. In case it turns out that this item is damaged one may purchase another one to replace it provided it works well thus eliminating the problem.

Check the Flue for Blockages: One has to see if anything blocks smoke discharge ducts through which carbon dioxide escapes from fireplaces. After removing these objects you should start your heating device again and make sure whether everything is fine or not at present time.

Evaluate Flue Installation: Improperly done installation work on how gases for venting purposes exit the appliance may result in such factors as abnormal temperatures causing an A2 fault code.

Clear Condensate Pipe Blockages: Check if there is any ice or blockage of condensate pipe by debris because that will cause a malfunction in the system. This can be rectified either may thawing a frozen condensate pipe or removing obstacles causing faults.

Consult a Professional: In case of problems with flue and exhaust system, it is advisable to have licensed Gas Safe experts who can identify and eliminate the A2 fault at once. The expert will perform safety checks on flues , sensors and other related components in order to ensure they are functioning well.

Regular Maintenance: To avoid repeating this issue in future, one should seek for the services of technicians on regular basis. For instance, during annual servicing one can easily detect malfunctions within flue systems, sensors and other significant parts before they become faulty.


The A2 fault code on a Viessmann boiler is a grave indicator with respect to its flue gas or exhaust system which ought to be treated as soon as it comes up. Homeowners take responsibility for simple inspection and solving problems, but since these issues are extensive and unsafe there should be professional assistance from specialists who deal with them. Regular maintenance of boilers helps early detection of possible problems that may affect your home heating system’s reliability or safety performance.