Exhaust ducts must always be laid rising from the Truma heater towards the cowl.
If the exhaust gases from your Trumatic S still pass through an aluminium pipe, replace this with a stainless steel pipe.
How to tell the difference:
When you remove the cover, you see a short exhaust duct. If the exhaust duct has a coil, it is stainless steel. If it does not have a coil but only has small grooves, it is made from aluminium and must be replaced.
Please note that the pipe must be replaced by an expert (e.g. Truma service partner).