Clean the filters on the main line and multiblock.Check the burner gas tip.Perform insulation measurements of ignition and ionization electrodes; replace electrodes should there be leakage to the body.Check ignition cables and sockets.Check all wiring points. Tighten loose connections.Clean the dust and layers accumulated on the fan and air klappes.Check gas line pressure, it must be the same with the first adjusted pressure, otherwise burner load and emission values will also have changed.Check all bolts of the burner and SHG. Tighten loosened bolts