Sensor Readings Seem Wrong: Sensor-by-Sensor Diagnosis

Wrong sensor readings fall into two completely different categories: placement errors (the sensor is working correctly but measuring the wrong thing because it's in a bad location) and actual sensor failures or calibration drift. The fix is completely different for each, so the first step is always to determine which category you're dealing with.

Temperature Running Too High

This is by far the most common complaint, and it's almost always a placement problem rather than a sensor failure. The diagnostic test: check your temperature at 3:00 AM on a calm, clear night and compare it against the nearest official ASOS station (available at aviationweather.gov). If your reading is within ±2°F of the official station at that hour, your sensor is fine — your afternoon high readings are artificially inflated by solar radiation errors from your placement. The fix is moving the sensor to a better location, not adjusting calibration. Read our complete radiation shield placement guide for the specific rules.

If your temperature reads high even at 3 AM, you have an actual sensor issue. Common causes: the radiation shield has cracked or yellowed (UV degradation turns white plastic yellow-brown, which absorbs solar radiation even at night through thermal mass), moisture has gotten into the sensor itself (check for condensation inside the shield), or the sensor has developed calibration drift (apply an offset correction in WSView Plus or your station's app under Sensor Calibration).

Temperature Running Too Low

Consistent low readings are less common than high readings but have specific causes. If your station is in a low-lying area — a yard depression, a valley, near a drainage channel — cold air pools at night and can produce readings 3–8°F below flat-terrain stations. This is your real microclimate, not an error. More problematic: if the sensor wicks moisture (common when mounted too close to vegetation or in an area of heavy dew), evaporative cooling can reduce readings by 2–5°F on humid mornings. Ensure the radiation shield has adequate clearance from any vegetation.

Rain Always Reading Zero or Far Too Low

If your rain gauge reads zero through an event you know produced measurable precipitation: (1) Check the funnel screen for complete blockage — a film of pollen, spider web, or leaf debris can seal the funnel entirely. Remove the funnel cap and inspect. (2) On wireless sensor stations, verify the rain gauge sensor is still paired to the gateway — in WSView Plus, check that the rain sensor signal strength indicator is present and not zero. (3) Test the tipping mechanism manually: pour a small amount of water into the funnel with the funnel cap removed and listen/watch for the tipping bucket to activate. No tips with water in the funnel means a jammed mechanism or a broken tip sensor reed switch.

If rain reads low but not zero: check placement. A gauge in a wind shadow (see rain gauge placement rules) can consistently catch 15–25% less than actual precipitation. Also verify gauge level — a 5° tilt causes systematic under-reads on one side.

Wind Always Zero or Stuck on One Value

Wind speed stuck at zero: for cup anemometers, spin the cups by hand — if they feel stiff or won't turn freely, the bearing has failed or is jammed with debris. If cups spin freely, check the sensor cable connection at the console or gateway junction. On Ecowitt stations with wireless sensors, verify signal strength in WSView Plus. For ultrasonic anemometers (WeatherFlow Tempest, some Ecowitt models), inspect the transducer faces for spider webs or insect debris — this is the most common failure mode and is resolved by gentle cleaning with a soft brush.

Wind stuck on a constant non-zero value (e.g., always 5 mph regardless of conditions): this usually indicates a failed anemometer bearing that's providing a constant pulse signal rather than varying with actual rotation. Replacement anemometer heads are available from manufacturers for $15–$35.

Humidity Stuck at 99–100%

A humidity sensor reporting 99–100% continuously when conditions don't justify it is usually a contaminated or saturated sensor. Capacitive humidity sensors can become permanently saturated if exposed to condensation for extended periods — common if the radiation shield has moisture ingress or if the station was stored without ventilation. The recovery procedure: remove the sensor from the shield, place it in a dry environment (low humidity room, not in direct sunlight) for 24–48 hours. If it normalizes, the shield has a moisture ingress problem to address. If it remains at 99–100% after full drying, the sensor has failed and needs replacement.

Barometric Pressure Wildly Wrong

A pressure reading dramatically different from regional values (more than 0.5 inHg / 17 hPa off) is almost always an elevation setting error, not a sensor failure. Verify the elevation entered in your station's app settings matches your actual elevation to within 50 feet. A 100-foot elevation error produces roughly a 0.11 inHg sea-level pressure error. Recalculate using a GPS app or topographic map, re-enter, and verify against an airport altimeter setting. See the detailed calibration procedure in our accuracy guide.

UV Index Always Zero or Unrealistically Low

UV sensors are among the most fragile components in consumer stations. They can be blocked by: dirt or pollen accumulation on the sensor dome (clean with a soft damp cloth), UV sensor dome degradation (the acrylic dome yellows with UV exposure over years, blocking the very radiation it's supposed to measure), or sensor failure. The UV sensor is often a separate module from the main thermistor assembly — on Ecowitt stations, the UV sensor is in a small dome on top of the sensor array and can be replaced independently of the full sensor suite.