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Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your
issue. First I’ll need some more info so I have a more complete picture of your situation.
What do you have for an aquastat/relay? do you have a multi-meter?
The Taco control is a zone control not the aquastat relay. You can't troubleshoot this without a meter
Possibly a control issue depending on what you have for a burner ignition control. If it's an R7184 or R7284 you could see the LED light up even if the aquastat/relay was malfunctioning. Can you give me a model for the aquastat relay? If not is it digital?
Sorry it took so long to get back to you. I logged off for the night before you posted your last response. Let me know if you want to continue
I'm logging off soon but we can start on this. First jump the thermostat terminals on the L8148. That would be T & T or T & TV top of the control. Once you do that check for 120 volts AC at the B1 & B2 terminals. If you have 120 v there then you probably have a bad burner ignition control but you first need to verify that you have 120 v to the burner motor. If you don't have 120 volts at B1 & B2 with T T or T TV jumped and the boiler is cold then the L8148 is no good.
If you do have 120 v at B1 & B2 and you have 120 v to the burner motor but the burner doesn't run then you have a bad burner motor. I doubt you'll be able to do all this before I log off in a couple minutes so get back to me tomorrow if you need more help or tell me what you found.
Ok, you have to remove the ignition control from the junction box on the burner then locate the 2 wires going to the motor. Remove the wire nuts if it's an older control but leave the leads connected then test voltage there. If you have a newer control probe the terminals where the motor leads are connected.