Hi, I am a new form member. I just purchased a home that has an oversized spa with a Jandy LT400N-L Pool Heater. The issue I am having is no gas flow to the burner. I have confirmed no 24 VAC to the gas valve. After each attempted start the exhaust fan runs for about a minute then it stops and the "Service" light comes on. After 3 attempts the “Air Flow” light comes on. Since there appears to be lots of airflow it seems likely it is either a faulty pressure switch or a plugged vacuum line. BTW, I am a General and Electrical Contractor so even though I am not familiar with pool heaters specifically I have worked on similar equipment in the past. My problem is figuring out how to access things. The right side and the back are 6 inches from a block wall so I would have to get access thru the front, left side, or top. Any suggestions on how to go about this would be greatly appreciated. Thanks in advance.