heater won't stay on
I got up this morning and noticed that it was a little chilly in the house and went to the thermostat and saw the house was about 62 and the therm was set for 66 but the heater was not on. I raised the temp and the heater dtill would not turn on so I cycled the on/off switch and heard the motor click on, I noticed when I walked by a vent that there was cool air coming out of the vent. I went down stairs to check to see if I could see the gas flames. None. I cycled the main on/off switch on the unit. I heard it click on and saw the ignitor heat up and then the gas came on and lit, the flames stayed on for and 5 sec and then clicked off, the ignitor heated up and relit but clicked off again. It didi this 3 times then would not try again. I thought maybe the filter was an issue so I turned the unit off and replaced the filter, turned the unit on. I stood there and watched the ignitor heat up and then light the flames, I stood there for about a minute, it stayed lit so I figured the filter was the issue. I went off and took my shower and the house had warmed up. So off to work I went feeling that I fixed the problem.
Well my wife just called and said that the heat isn't working. I had her set the temp up on the thermostat, the motor would come on but blow cool air and not hot. I had her go down and flip the main switch of for about 30 sec and then flip it back on and had her stand there to see if the flame stayed lit (yes it did).
My question is why won't it stay lit when it comes on by command of the thermostat? It seems to go thru 3 cycles and then the ignitor does not light up (seems like a safety feature) but it will work when the main switch is cycled on/off till the next thermostat command to come on? This system has been working well till now. Thanks in advance for any input on this.