I have a model 90N75A serial # 04013617. It was installed in 2005 I believe. Beginning last year we have had considerable trouble with it not turning on. We replaced the gas valve, the termostat (3 times), and still have many mornings with no heat. Our repairman doesn't know what else to do for it. We have beenaout a great deal of money trying to fix it. What can you tell me that will help? Thanks much, danwacker@gmail.com