Hey everyone I have a Homedics TotalClean 5-in-1 model that I bought about 14 months ago and suddenly the red light started blinking a few days back. The unit still runs and blows air but that annoying red indicator stays on no matter what I do. I already cleaned the filter with a vacuum and it looked pretty dirty but the light did not reset. I tried unplugging it for an hour and plugging back in and still nothing changes. It is in my bedroom so the constant red glow at night is driving me crazy 
. I looked in the manual and it just says red means replace filter or check UV bulb but both seem fine to me. Has anyone dealt with this exact issue on a Homedics purifier? How do I make the red light go away for good without buying a whole new unit? Any reset tricks would be amazing thanks in advance!
I had the exact same problem with my AP-T40 last year. The red light is almost always the filter replacement timer even if the filter does not look that bad yet. HoMedics counts running hours and after around 3000-4000 hours it forces the red light no matter what. The trick that worked for me is hold down the power button and the UV button together for about 8-10 seconds while it is plugged in. You should hear a beep and the light flashes then goes back to blue. Worked like a charm and I got another 6 months out of the same filter.
Mine was doing the red blinking thing too and it turned out the UV bulb actually burned out. You can check by turning on the UV function in a completely dark room and looking through the side vents. If you see zero purple glow the bulb is dead. Replacement bulbs are like 15 bucks on amazon just search Homedics UV-C replacement. Super easy to swap just unscrew the bottom plate. After I put the new one in the red light disappeared immediately no reset needed.
I fought with this for weeks. Tried every button combo people mention online and nothing worked. Finally called Homedics support and they told me on some batches the reset is different. You have to unplug it completely then hold the filter reset button (the tiny one on the back near the cord) while plugging it back in and keep holding for 15 seconds. Red light flashed three times and turned off. Saved me from throwing it away.
My red light came on because the pre-filter cage was not clicked in all the way after I cleaned it. These things have sensors that detect if everything is seated properly. I took the whole front off again aligned the tabs perfectly and pushed until I heard two distinct clicks on both sides. Turned it on and the red was gone instantly. Always check that first before you buy new parts.
Same issue here but mine was stubborn. The standard resets did not do anything because I had already replaced the filter with a third-party one and the unit did not recognize it. Ended up having to do the factory reset which erases the timer completely. Press and hold the power button for 20 seconds until all lights flash then release. It beeps twice and restarts like new. Red light finally gone and it accepted my cheap amazon filter.
Just adding my experience in case someone has the pet version like me (AR-10PET). The red light on those can also mean the carbon pellets tray needs to be refilled or replaced. Mine was completely empty after a year with two cats. Ordered the refill kit for like ten dollars and once I topped it off the light turned blue again. Worth checking if you have smell control model.
I see this question every few months 
. Short answer is 95% of the time it is the filter timer. The other 5% is either UV bulb or the unit thinks the door is open. Quick test: take everything apart wash the permanent pre-filter if yours has one then put it all back super carefully. Then do the 10-second power + UV hold. If that fails buy a genuine Homedics filter even if you hate the price because third-party ones sometimes do not reset the sensor properly. Been there done that.
Okay this is going to sound ridiculous but it worked for me twice now. My red light kept coming back after reset because the unit was on a slightly uneven nightstand and the internal tilt sensor thought something was wrong. Moved it to a completely level surface and the light has stayed blue for months. I know it sounds crazy but these newer models have all kinds of sensors HoMedics never tells you about.
Had this on my moms unit last weekend. We tried every reset under the sun and nothing. Finally opened it up and noticed one of the tiny wires to the UV bulb had come loose from vibration. Gently pushed it back into the connector slot put it together and boom no more red light. If you are comfortable opening the bottom panel check the wiring first before spending money.
Thanks for all the tips everyone! The power + UV hold for 10 seconds did it for me 
Light is finally blue again and I can sleep without that creepy red glow.
Update: bought the official filter and it reset automatically no button pressing needed. Lesson learned stick to OEM filters with these things.
Just wanted to say thank you the tilt sensor thing fixed mine lol who knew