I just installed a new circuit board on my Carrier heater. I ran the component test sequence and the LED light blinks fast several times (estimate 40x) what problem does that indicate?

Do you have two transformers in these units? That would be one for the heater and one in the AC unit. Also, check that you have a good ground and that screws on all connections are tight, like on the breakers and on the ground and neutral in breaker box. They loosen over time. I would check all breakers for tightness while you have the box open. If you have two transformers and they are out of phase they will short out. You will have to switch one primary voltage source lines so that you are not reading 24 volts between transformers. Why did you replace the circuit board and what caused it to fail? They don't just fail without something else making it fail. Unless you want to buy boards regularly you have to find the cause. Was any other work done before the failure? DrTom4444