I have a Laars LX Pool heater. I just opened up my pool for the summer and encountering an issue with the heater (everything worked just fine last year). When the pump is running and the heater is turned on everything works just fine. The heater will heat until the target temperature is reached. When my pump timer goes off and the pump shuts off, the heater used to say "Low Pressure" and turn itself off, but now it displays "Service AGS" error. When the pump comes back on it doesn't get out of the "Service AGS" mode and never kicks back on. If I turn the heater off and back on, it kicks right back up and starts heating again.
The service manual isn't helpful at all, everything regarding "Service AGS" refers to gas issues and blockage, but the heater works just fine as long as it's turned on after the pump is on so I doubt it's a gas issue. I suspect something is going wrong with the pressure switch and the heater isn't turning itself off when it notices low pressure?