I have a Pentair MasterTemp 400 heater for my spa. Recently the heater will not fire when the eater temperature falls below the set temperature. I rebooted the system & the blower came on, but again the heater would not fire. There were no error codes on the heater's display; only the illuminated Service Heater light. On the underside of the display the AGS light was on.
I checked the thermal regulator & discovered that it would not open. I replaced it with a new unit, but still the heater would not fire. Also, there were no flashing lights on the Fenwal unit. (In addition, I might add that the thermistor was replaced 5 months ago. when the same problem occurred. I seems unlikely to me that it could have gone bad so quickly). Anyway, as I was looking at the heater components, I switched the On/Off switch on the gas control value to OFF & then to ON. Surprisingly the heater fired up & continued to run until the set temperature was reached. But to my disappointment when the pump started up the next morning, again the heater would not fire. Cycling the ON/OFF switch on the gas control value wouldn't restart the heater.
So, any thoughts that you might have would be most appreciated. I am reluctant to simply start replacing parts until the issue is resolved. Thank you so much.
I checked the thermal regulator & discovered that it would not open. I replaced it with a new unit, but still the heater would not fire. Also, there were no flashing lights on the Fenwal unit. (In addition, I might add that the thermistor was replaced 5 months ago. when the same problem occurred. I seems unlikely to me that it could have gone bad so quickly). Anyway, as I was looking at the heater components, I switched the On/Off switch on the gas control value to OFF & then to ON. Surprisingly the heater fired up & continued to run until the set temperature was reached. But to my disappointment when the pump started up the next morning, again the heater would not fire. Cycling the ON/OFF switch on the gas control value wouldn't restart the heater.
So, any thoughts that you might have would be most appreciated. I am reluctant to simply start replacing parts until the issue is resolved. Thank you so much.
