I have an intertherm furnace in a mobile and it goes off on pressure switch open . Icleaned the ports on the inducer motor then I changed the pressure switch and then the motor . Ivacuumed out the flue pipe bythe way this unit is coming up 3 years old. I then used silicone on the top and bottom of the motor housing thinking it was not producing enough vacuum po the one port and enough inchs of wc pressure on other. It has new hoses and a new chimney . It is very frustrating because the people that put it in won't return my calls any more they told me its normal for it to fail every 1-2 days . Iturn the power off blow though lines and it usually starts and runs ater 2 or 3 tries for 1-2 days cycling nomaly for that time any ideas