Topic: Ecowitt WH41 Air Quality Sensor (PM2.5) only reading low

[theslydog]

Has anyone run into this problem?

I have a Ecowitt WH41 and it is just sitting on 3-4ug/m3 no matter what the actual AQI is.

IE there is currently a fire in our area and a hand held is reading 100ug/m3 similar to the offical AQI website but the Ecowitt is reading 3ug/m3.

Is there any reset or a part than can be replaced?

Or is the unit now US?

The Unit was purchased in the middle of 2019 and seems to have started this behavior b4 Christmas.

[davidefa]

I don't know if this is your case but I stumbled in this video ( as I was searching how to mount my PMS7003 to prevent dust build up on the sensor )
Even tough the WH41 sensor is different, these low cost sensors are similar, so the problem could be dust build up, a malfunctioning fan...

P.S. I don't know how to trust a sensor after such a cleaning...
P.P.S. Here a small comparison of a few sensor, the oldest sensors show sign of 'fatigue'
So this is to be expected with time...

[theslydog]

I don't know if this is your case but

The Ecowitt uses a Honeywell sensor.
Anyway it stays on 3-4ug/m3 even with the sensor disconnected.

So definitely a problem somewhere.

Just to let everyone know Lucy sent me a replacement for this faulty one at no charge.

I thought the new one was also not working, but it is fine.
It was sitting on 0ug/m3 for a bit, but it was just that the original I had never ever went to 0.
So the original may have been faulty from the beginning.

[kc2kzz]

I will say that Ecowitt has been good at replacing these.  My original one, which worked fine for 6 months,  started to report only 11 ug/m3 regardless of what the actual reading was.  The first replacement was bad also due to a bad antenna/board.  The 2nd replacement appears to be working great.

[dolfs]

My problem was that recently (see below) my WH41 was reading excessively high values, in particular during high humidity. After seeing the video referenced above I cleaned the inside of the unit as best I could. It is not easy to get the level of access like shown for the Plantower units, but by removing the white "air" cover (clips on the side) you can get access to the sensor package. It has three rubber feet you can remove to be able to remove one cover. This gives you some access to the air inlet channels, which I cleaned with compressed air. You are also able to left the fan out to clean it. Mine didn't look dirty but I cleaned it. Access to the photo diode was not possibly using this method.

Perhaps more importantly I looked up the sensor manual and it speaks about correct, and incorrect, mounting. Basically if using the ecowitt unit on a flat horizontal platform you are going to be fine no matter orientation. If you are mounting on a vertical surface you should be mounting in such a manner that the air inlets are lower than the fan (outlet). See attached image.
To do this correctly, remove the white outer shell from the base and, issuing a flashlight or such to peek inside and located the fan. It easiest to then mark it on the white outside or inside with a sharpie or such. To get the right orientation against a vertical surface you must then mount the unit in a vertical orientation, not horizontal as I had it.

In my case this can also be remembered by making sure the internal USB port is on the top side, but I am not sure all units are manufactured identical in this manner.

After a brief test, inside the concentration dropped from some 160 µg/m³ down to 11 so it seems to be a huge improvement. No going to put it back outside to see what happens (humidity is higher than inside).

P.S. The "recently" above was after having the unit removed due to a painting job. I had it mounted on a vertical surface, but horizontal orientation. I may well have put it back 180 degrees rotated from how it was before, reversing between up and down for air inlet and outlet, which could easily have a detrimental effect. After some more testing I am going to mount it, still on a vertical surface, in the vertical orientation.