I have an issue. I have a Jandy 400k BTU pool/spa heater that I'm trying to get back running. Here's my story. Bought the house last year, got the pool up and running, the heater had two 120 gallon propane tanks connected to it, both were empty when we bought the house. We had a house warming party and was able to run the heater to the spa using a standard 20lb propane tank (size of the one on your BBQ). It ran great, but emptied those tanks pretty quick! To try and save money I bought a taller, 100 lb tank and connected it to the system, the heater will fire up in start-up mode, but never fully run, shows an error "AGS". It ignites, runs for ~20 secs, then the blower turns up and it kills the flame. I then tried taking one of the 120 gallon tanks, had it filled up, and connected it to the heater, I get the EXACT same issue that I had with the 100 lb tank, same "AGS" error. I then hooked up my small 20 lb tank, and the heater fires right up! What is going on!?