I have vaillant boiler problems and would like some help on troubleshooting the issue. I have a vaillant ecotec plus 824 and randomly the boiler does not ignite the burner. I get the fault s.33 where the vaillant boiler manual tells me it is a problem with the air/flue system. I have had a service guy check the boiler twice and the problem always comes back. Any help would be greatly appreciated
The problem with your boiler is the air pressure switch located on the top of your boiler. Check out the parts diagram here.
This part has a diaphragm that has become blocked. During normal operation when the fan activated air is sucked through the flue and a small amount fills the diaphragm and makes the electrical contacts within the switch. In your case the flue is blocked and air is not inflating the diaphragm, your diaphragm has a hole, or your contacts are perished. I would advise you get a corgi man to replace this part to ensure ongoing reliability of your boiler.