Hello, it comes straight 40 cm and there an elbow makes it enter the wall and there it has another elbow and there it makes it avoid the eaves and then if it goes up and passes the roof
I would believe that there is the problem. The first section must be at least 1 mt and then the distances with curves or elbows of 45 ° are saved. As for testing and just for testing, bridge the sensor terminals. If the heater is running well you will have to recondition the gas outlet.
In principle it seems that the problem disconnected the output and ventilate and arrived at 4 minutes until the sensor acted ... so thank you very much !!!! I will install with more than one meter and it will surely work .... too much is telling you ... capooooooooo ... hug.