I have a Weber S-670 natural gas grill. For the last couple of months, the grill will not heat up after dark, when temperatures are lower. During daylight hours and higher temperatures, the grill works fine. I have contacted my gas supplier and they maintain I have a malfunctioning grill, not low gas pressure. I have had two separate Weber repairmen check the grill, during daylight, and they tell me the grill works as it should. Not sure how to increase pressure to the grill during neighborhood heavy gas usage. Any suggestions appreciated.