Maytag 4000 series model mhwe450ww

[Vcarlo]

I have the 4000 series maytag front loading washer. I got an f21 error. Checked the drain pump and there was nothing there. Checked all hoses and cleaned them all. None are kinked or damaged. Unplugged the washer let it sit for a few minutes. Plugged back in ran a drain and spin cycle. It worked fine. Tried to run the rinse and spin cycle got the f21 error code again. Then I replaced the drain pump with a brand new one. Ran a rinse and spin cycle and it worked fine. I tried a second rinse and spin cycle a little while later and it popped up with the SUD error code. The washer added more water and continued on only to then read the f21 code again a few minutes later. I have no idea what to do now and I really need help or ideas of what it could be please! I have checked and there is nothing in the drain and all the hose are still clean and not kinked. If anybody can think of ANYTHING I would greatly appreciate it. Thank you!

[johntech]

Is there water in the tub when you get the error? Does the pump run before getting the error? I would hook a shop vac up to the drain hose right after it fails and try to suck water out. If you can't get water out then it has a clog. Did you pull the rubber boot off the bottom of the tub when cleaning the drain lines? 

[certified tech group 51]

I would check the pressure switch W10271610 and the hose 8181739........main control may be getting incorrect water level  reading from  from the switch or restriction in the hose....

[sh2sh2]

When it gives the f21 is there still water or is it all drained?