LG F1403RD washer/dryer, dryer not heating up

First of all welcome to all ,

I have a F1403RD LG washer dryer but the dryer has suddenly stopped heating up. At first I would get error DHE roughly on 19 minutes into a 30 minute dry only setting.

After the error I replaced the dryer element and the Thermister dryer sensor the 2 prong job with parts from 4lg. I didn't replace the Thermostat in the metal dryer duct so could it possible be this? also, how do I test this ?.

even after both replacement parts were installed It still doesn't heat up on dry but the DHE error doesn't appear anymore and it goes to the end of the dry only cycle as normal but cold.

I also took the plastic vent dryer duct off the back of the tub and cleaned it out but there wasn't much in it as I had cleaned this about a year back.

I'm now at a loss as to what the problem can be. How do I now check to find out what's causing the error ? any fuses or blocked pipes I should look for ? Any help would be greatly appreciated.

thanks