My infrared heater home heater makes a screeching noise

It may be getting too hot and activating the safety shut off. This may need a new board. I have never worked on one of these but it has to be fixable. Depending on the cost of the unit as to whether or not it is worth it.

Check to make sure that the elements are weird in the right place.
See if there is any loose screws or metal on metal.
The elements might be bad
If wired wrong it may not be making a proper circuit.
Check the pcb boards to see if it is touching metal on the bottom side of board.
If you put a screw in the wrong spot it may be grounding something out.
Check all wires for bare spots

If it is clean it should not.

first check the outlet its plugged into to be sure there is actually power there, if not check your breaker box, it may have overloaded the circuit and popped the breaker. if all good there, check the unit for a fuse, which may be blown.

The level sensor inside might be loose or fell off. Call the company.

Does it matter if the thermostat is 120v or 250v?

I would read the customer reviews on this product , looks like nearly 70% of consumers are less than happy with this unit.

1500 watts is the units peak output, and drops to around 600 as it warms up. My hair blower puts out more power.

1500 watts is LESS than the output of a small element on your stove top. The real measure of heat is not watts, its BTUs and btus from gas are much cheaper than they are from electricity.

Replaced 301 80C 16A thermostat, purchased on ebay for $6.00, fixed problem. to Fix standing at front, Remove left side panel, two small screws hold thermostat in place. LifeSmart wants $36.00 for same part. Fixed problem.

Remove power for some time and switch on after few hours , this might reset any error on the processor , if not the error could be due to fault indication of a failure within the heater, could be the infra or the element.