theres your first clue with a temp control machine, just turning off the cold water will not deliver a hot wash.....
many machines will pause with an error code if both faucets are not turned on....yeah, theres a sensor for that alone.....this makes it hard to test certain machines with a garden hose out in the garage...
and machines with the auto temp will fill with hot until it gets too hot and then calls for the cold to be added, so may not be a good idea to turn the cold side off...for some, you can get away with turning the cold water down to a trickle....again, each machine is a little different in the way it reacts.....turning the water heater up can reduce the dubbed down temps
there are ones that when hot is selected, will add for only 60 seconds, and then the rest if either warm or cold added......and you can't by-pass a lot of this stuff....
for some, and may not be practical for your setup, but install a 'y' valve and hose on the hot side faucet, and fill the machine manually with hot water, then turn that off, and let the machine resume with the cycle....
the more we try to by-pass on these newer machines, the more they make it difficult to do so...
some machines you can unplug that temp sensor.....others are smart and wont operate if it is unplugged....others you can leave it plugged in, but depending on the setup, pull it out of the route to sense the temps....
theres a bunch of things you can try, until you find one that works for you best....
I even pulled the restrictor out of the hot side of the inlet valve, for a warmer mix....