Check you have not mixed up triac MT1 and MT2 pins. What is your capacitor value
I do not know "1K400V" looks like u1K400V = 0.1uF each.
It needs to be about 47nF with 500k potentiometer or 0.1uF with 250k potentiometer, with 120VAC.
I have had troubles with chinese triacs and potentiometers not working well or lasting long. Check your potentiometer is not burnt.
A better circuit adds a bridge rectifier to give "hysteresis free" or "no snapback" effect, like you see with lamp dimmers. It's also helps with inductive loads. The extra diodes discharge (reset) the firing delay capacitor every cycle.
More can be found in figure AN1003.12 or
Teccor App note AN1003This is the eBay circuit for the "4,000W SCR" dimmer.