I have a Monitor 422 that fails to turn on. When I first turn it on it complete the pre-burn purging cycle (3 minutes) and then the 4 lowest burner lights turn on and I can feel the lower part of the combustion chamber begin to heat for another ~ 3 minutes. After this, all burner indicators are flashing on and off until the cool down cycle completes and the system turns off. Any idea what the problem might be?