We have a Heatilator ND3630I unit that was installed a few years ago. We only ever used the unit once during a power outage last year and had no problems. Now we have started using it and have found that after anywhere between 7 and 45 minutes, the flames go out completely but the pilot stays on. We have to get up and turn the wall switch off and then back on again to get the flames to come back on. We have tried waiting it out to see if the flames come back on their own but they never do. We do have the new PSI ignition system. It seems to be grounded but we have not had a chance to check the actual voltage usage yet. Has anyone experienced this problem or have any ideas? It does the same regardless of if it is running off of the wall switch or the batteries.