Scale Won’t Zero, Drifting or Stuck in Calibration Mode: How to Fix It
Reviewed by MNM Scales technicians · Updated October 27, 2026
Short answer: if a scale is stuck in calibration mode, turn it off and back on without saving; on many indicators the TARE or ZERO key also backs out of the menu. If it won’t zero, clear the platform, check for debris or anything touching the deck, and restart with nothing on it. If it drifts, let it warm up, then check the cable and junction box for moisture or damage. If none of that fixes it, a load cell or the calibration needs a technician. Do not change settings you are unsure of: an accidental setting change is one of the most common reasons we get called.
After more than 30 years of repairing scales, since 1992, our technicians see the same few problems again and again: a customer pressed the wrong key and entered calibration mode or changed a setting, a load cell failed after heavy use, or a cable was cut or crushed. This guide walks through the checks in the order we do them, so you can fix the simple causes yourself and know when to call. It applies to floor, bench, platform and hanging scales, the kind used every day by food manufacturers, grocery stores, seafood businesses, steel and metal producers, chemical plants and shipping docks.
Quick diagnosis: symptom, likely cause, first fix
| Symptom | Most likely cause | First thing to try |
|---|---|---|
| Display shows CAL, SETUP, P1, F1 or similar | Calibration or setup mode entered by accident | Power off and on without saving |
| Won’t return to zero after a load | Debris, something touching the deck, or zero range exceeded | Clear the platform and gaps, restart with nothing on it |
| Weight creeps up or down with nothing on it | Warm-up, moisture, damaged cable or failing load cell | Warm up 15–30 min, then inspect cable and junction box |
| Reading jumps around | Vibration, air movement, loose connection, cut cable | Steady the scale, then check connectors and cable |
| Different reading in each corner | One load cell or the junction box trim is off | Corner test; call for service |
| Error code instead of a weight | Overload, underload, unstable weight or a cal error | See scale error codes |
| Display blank or flickering | Power: adapter, battery, cord | Try a known-good adapter or fresh batteries |
Stuck in calibration mode
This is the most common call we get. Most indicators reach calibration or setup through a key combination, a hidden button or a switch behind a seal. It is easy to press them by accident while cleaning or tapping keys, and the display then shows something like CAL, SPAN, SETUP, P-something or F-something instead of a weight.
- Do not press keys to “see what happens.” On many indicators, the next key press saves a new zero or span.
- Turn the indicator off and back on. Unsaved changes are usually discarded at power-up.
- If it comes back in the menu, look for an exit or escape step in the manual. On many indicators, TARE, ZERO or a key marked REWEIGH or ESC backs out without saving.
- Check the weight with a known object. If the weight is now wrong, a setting or the calibration was changed, and the scale needs a calibration.
- Call us before changing settings. Divisions, capacity, filtering and zero tracking all affect accuracy, and legal-for-trade scales must not be adjusted without a re-inspection.
A CAL.Er, Err or similar message during calibration usually means the test weight was unstable, too light for the indicator’s minimum span, or a different value than the one entered. Model-specific steps are in guides such as LP7515 indicator calibration, and the general procedure is in how to calibrate a floor scale.
Scale won’t zero
The ZERO key, and the automatic zero at power-up, can only remove a limited amount of weight, a small share of capacity. Indicators for legal-for-trade use are limited by NIST Handbook 44. If there is more than that on the platform, or something is pushing on it, the scale will refuse to zero or show an error.
- Clear the platform. Remove everything, including mats, pallets and buckets left on the deck.
- Check the gaps. On floor scales, dirt, ice, packed debris or a pallet jack wheel in the gap between deck and pit or frame holds the deck up. Clean the gaps all the way around.
- Look under the deck. Something wedged under it, or a deck that has shifted against a stop, changes the reading.
- Restart empty. Turn the indicator off, make sure nothing is on the scale, and turn it on again.
- Still off? A load cell that was overloaded or shock-loaded can take a permanent “set” and no longer return to zero. That needs a technician.
Scale drifting or creeping
Drift is a slow change in the reading with nothing changing on the scale. A little movement in the first minutes after power-up is normal while the electronics warm up. Steady drift after that has a cause:
| Cause | How to tell | Fix |
|---|---|---|
| Warm-up | Drift settles after 15–30 minutes | Leave the indicator on, or power it up earlier |
| Temperature change | Drift follows sun, doors or heaters | Shade the scale; recheck zero as temperature changes |
| Moisture in junction box or cable | Worse after washdown or rain; corrosion inside the box | Dry and reseal the junction box; replace damaged cable |
| Damaged cable | Reading changes when the cable is moved | Replace the cable; recalibrate |
| Failing load cell | Drift stays after the checks above; one corner reads off | Test the load cell; replace if needed |
| Air and vibration (bench and lab) | Small scales jump with fans, doors or machinery | Move the scale or shield it; use a draft shield |
Readings jump or won’t settle
A reading that jumps between values usually means the indicator is seeing noise. Check that the scale is on a solid, level surface, away from vibrating machinery and fans. Then wiggle the cable gently where it enters the indicator and the junction box: if the reading jumps, the cable or connector is the problem. Cables that are cut, crushed by a forklift or chewed through are among the most common repairs we do. Loose terminal screws in the junction box do the same thing.
How to do a corner test
If the scale reads differently depending on where the load sits, one load cell or the junction box trim is off. A quick check:
- Zero the empty scale.
- Place the same test weight, about 10 to 25 percent of capacity, over each corner in turn, close to the load cell.
- Write down each reading. On a healthy scale, they agree within a division or two.
- If one corner reads high or low, note which one and call us. Adjusting junction box trim needs care, and the scale must be recalibrated afterwards.
What “accurate enough” means after a repair
For commercial Class III scales, NIST Handbook 44 sets the tolerances a scale must meet in service, counted in scale divisions (d). Acceptance tolerances, for new or newly repaired equipment, are half of these.
| Test load, in divisions | Maintenance tolerance | Acceptance tolerance |
|---|---|---|
| 0 to 500 d | 1 d | 0.5 d |
| 501 to 2,000 d | 2 d | 1 d |
| 2,001 to 4,000 d | 3 d | 1.5 d |
| Over 4,000 d | 5 d | 2.5 d |
Example: a 5,000 lb floor scale with 1 lb divisions, tested with 1,000 lb (1,000 d), may be off by up to 2 lb in service.
When to call a technician
- The scale still won’t zero or keeps drifting after the checks above.
- One corner reads differently from the others.
- The scale was overloaded, dropped or hit by a forklift.
- Settings or calibration were changed and the weight is now wrong.
- The scale is used for selling by weight: after any repair or calibration, it must be placed back in service by TDA-registered technicians in Texas.
Our technicians repair scales in our Cypress, TX shop and on-site (see scale repair in Houston). On-site service is $295 plus $2 per mile, round trip, charged once per visit, with calibration priced per scale. For floor and crane scales, our technicians bring their own certified test weights (see on-site scale calibration and crane scale calibration). Need a scale while yours is in the shop? We rent all types of scales: see scale rentals.
Calibrate once it is fixed
After a load cell, cable or indicator is replaced, or a setting is changed, the scale needs a calibration. Bench scales and balances can come to us by mail-in calibration, usually done within 1–3 business days after we receive them. Choose the tier by the scale’s maximum capacity; see how often a scale should be calibrated to plan the next one.
| Maximum capacity | In-house calibration with certificate | NIST calibration with NIST-traceable certificate |
|---|---|---|
| Up to 2.2 kg (about 5 lb) | $95 (add to cart) | $395 (add to cart) |
| Over 2.2 to 6.2 kg | $195 (add to cart) | $495 (add to cart) |
| Over 6.2 to 35 kg (about 14 to 77 lb) | $250 (add to cart) | $595 (add to cart) |
| Over 35 to 150 kg (about 77 to 330 lb) | $350 (add to cart) | $750 (add to cart) |
| Over 150 kg (floor and large platform scales) | $495 (add to cart) | $995 (add to cart) |
Why buy from MNM Scales
- Repairs, parts, calibration and rentals from one company, with phone help when a scale stops working
- One of the largest scale distributors and an authorized dealer for the brands we sell, in business since 1992 (over 30 years)
- In-house calibration with a certificate, or NIST calibration with a NIST-traceable certificate; mail-in calibration also covers scales bought elsewhere and is usually done within 1–3 business days after we receive the scale
- TDA-registered technicians; on-site service in the Houston area is $295 plus $2 per mile, round trip, charged once per visit, with calibration priced per scale
- Scale rentals of all types of scales
- Order pickup at our shop, 21249 FM 529 Rd, Cypress, TX, by appointment
- Phone answered 24/7 at (832) 290-3120
Scale still not right? Call us with the make, model and what the display shows. Many problems can be solved on the phone; the rest we fix in our shop or on-site.
Frequently asked questions
How do I get my scale out of calibration mode?
Turn the indicator off and back on without saving. On many indicators, TARE, ZERO or an escape key also backs out of the menu. Check the weight with a known object afterwards, and call before changing any settings.
Why won’t my scale zero?
The zero key can only remove a small share of capacity. Clear the platform, clean the gaps around the deck, check that nothing is under or against it, and restart the scale empty. If it still won’t zero, a load cell may be damaged.
Why does my scale keep drifting?
Normal warm-up causes some drift for 15 to 30 minutes. Drift after that is usually temperature change, moisture in the junction box or cable, a damaged cable or a failing load cell.
Why does my scale read different weights in different spots?
One load cell or the junction box trim is off. Do a corner test with the same weight on each corner and call a technician if one corner differs.
What causes a CAL error during calibration?
Usually an unstable reading, a test weight that is too light for the indicator, or a different weight than the value entered. Steady the scale, use a certified weight and enter its exact value.
Can a damaged cable make a scale drift?
Yes. A cut, crushed or wet cable is one of the most common causes of drifting and jumping readings. If the reading changes when the cable is moved, replace it and recalibrate.
Does a scale need calibration after a repair?
Yes. After replacing a load cell, cable or indicator, or after settings were changed, the scale should be calibrated, and legal-for-trade scales must be placed back in service by TDA-registered technicians in Texas.
Do you repair scales on-site?
Yes. On-site service in the Houston area is $295 plus $2 per mile, round trip, charged once per visit, with calibration priced per scale. Repairs are also done in our Cypress, TX shop.