My 8 year old Minimax NT Lo Nox heater was dead. Checking voltages, I figured out that the transformer went bad. I replaced the transformer and now get power to the Digital Display Temperature Controller (DDTC). But now I get an E05 (ignition failure) message.
There are 4 LEDs in the back of the DDTC. The HiTemp, Tfuse, and Fan LEDS are lit. the PV LED is not lit. When the heater is turned on and it goes through startup sequence, the fan blows, the igniter gets red (can't see it directly, but can see the reflection in one of the burners), gas turns on, burners ignite and light for about a second, then turn off while the fan continues. Occasionally, when the burners light it will be somewhat explosive and flame will shoot out past the orifices. Most of the time, the burner light normally though.
I took out the burners and checked the orifices and cleaned everything up, but they weren't too dirty. This didn't help. I checked the resistance of the igniter/flame sensor and read 55 ohms cold. I took the wires off of the igniter/flame sensor and connected my voltmeter to them. There was low voltage during the first part of the startup sequence, and then it increased, but only to about 90 volts. My source is 240 volts.
Any chance this is the igniter/flame sensor gone bad? How can I check the flame sensor? It seems as though the igniter portion of the igniter works since the burners light. I'm hoping it's not the ignition control module, but 90 volts seems wrong. Then again, I'm not sure my test is valid since I removed the wires from the igniter/flame sensor.
Any thoughts are appreciated.