Thermostat working, pilot lights. I tripped the breaker to 'off', Ten minutes later turned tstat to 80, turned on the breaker. Pilot lit instantly with good flame. During warm-up time, several loud clicks at two different times. TWO minutes later, burners fired nicely. Lowered tstat and unit shut down normally. Raised tstat.... identical results. Eight hours later, got the call for no heat. Repeated above, pilot lit and burners never fired...no clicks this time. Luckily it's warm today! Please help!