Direct answer: The Watts WM100SM operating manual lists four numbered errors. Error 1001 is “unable to recognize start of regeneration,” 1002 is “unexpected stall,” 1003 is “motor ran too long, timed out trying to reach next cycle position,” and 1004 is “motor ran too long, timed out trying to reach home position.” The first fix the manual gives is a reset: press NEXT and REGEN together for 3 seconds, or unplug the power jack (black wire) from the circuit board and plug it back in. If the error returns, the causes it lists are foreign matter or high drive forces on the piston, a misaligned motor, gear, bracket or board, or a failed motor or board. “If other Error Codes display contact the factory.”
Publisher boundary: Water System Guide is an independent research publisher, not a Watts dealer. This page uses the Watts water conditioner operating manual with the WM100SM valve (FORM 0500-200, PDF created 2006) and the Watts Water Quality dealer catalog C-WQ-Dealer 2604 (April 2026), reviewed October 15, 2026. The codes apply to Watts softeners with the W100/WM100SM valve. Locksmith and twin-alternating controllers have their own documentation, which we did not find published.
Which Watts softeners this applies to
The WM100SM manual covers the “water conditioner with WM100SM valve,” and its specification table lists the M3011-W100SM through M3021-W100SM (WM100SM manual, PDF page 4). The 2026 catalog sells the current W100-valve models as M3011-CK10SM, M3013-CK10SM and M3015-CK10SM, plus the dual-media M3011-W100SM-CR-CMP (dealer catalog, PDF page 20). If your valve has NEXT, REGEN, SET CLOCK and arrow buttons, this page applies.
If your system is a Locksmith (model ending -L10SM, -L125 or -L10T) or a OneFlow, it does not; see our Watts water softener models comparison to identify it.
The four documented error codes
The manual’s “Troubleshooting Programming” table lists the problem “ERROR followed by code number” with these codes and a shared list of causes and fixes (WM100SM manual, PDF page 26):
| Code | Watts description |
|---|---|
| 1001 | Unable to recognize start of regeneration |
| 1002 | Unexpected stall |
| 1003 | Motor ran too long, timed out trying to reach next cycle position |
| 1004 | Motor ran too long, timed out trying to reach home position |
The manual spells “too” as “to” in the original; we have corrected the spelling.
Causes and fixes the manual lists
The manual does not assign causes to individual codes. It gives one list for all of them:
| Possible cause | Watts’ solution |
|---|---|
| Control valve has just been serviced | Press NEXT and REGEN for 3 seconds, or unplug the power source jack (black wire) and plug back in to reset |
| Foreign matter lodged in the control valve | Check piston and spacer stack assembly for foreign matter |
| High drive forces on piston | Replace piston(s) and spacer stack |
| Control valve piston not in home position | Press NEXT and REGEN for 3 seconds, or unplug and replug the power jack |
| Motor not inserted fully to engage pinion, motor wires broken or disconnected, motor failure | Check motor and wiring; replace motor if necessary |
| Drive gear label dirty or damaged, missing or broken gear | Replace or clean drive gear |
| Drive bracket incorrectly aligned to back plate | Reseat drive bracket properly |
| PC board damaged or defective | Replace PC board |
| PC board incorrectly aligned to drive bracket | Ensure PC board is correctly snapped on to drive bracket |
Step 1: reset the valve
The reset appears in three places in the manual. The general warnings say that after any maintenance on the drive or pistons, “press the NEXT and REGEN buttons for 3 seconds or unplug power source jack from the printed circuit board (black wire) and plug back in. This resets the electronics and establishes the service piston positions.” The display “should flash all wording, then flash the software version (e.g. 154) and then reset the valve to the service position” (WM100SM manual, PDF page 3).
The same reset also cancels an immediate manual regeneration: holding REGEN starts one that “the user cannot cancel,” except “by resetting the control by pressing NEXT and REGEN buttons simultaneously for 3 seconds” (WM100SM manual, PDF page 10).
After a reset, the clock may flash. The manual says the time of day flashes when “the NEXT and REGEN buttons were pressed to reset the valve,” among other causes, and the fix is to “reset the time of day” (WM100SM manual, PDF page 27).
Step 2: if the error comes back
A recurring 1002, 1003 or 1004 points to something stopping the piston or the motor. The manual’s list suggests this order, from simplest to most involved:
- Motor seating and wires. The motor must be “inserted fully to engage pinion.” Check for broken or disconnected wires.
- Drive gears. A “drive gear label dirty or damaged” or a “missing or broken gear” can cause errors. The manual lists the W100SM drive gear as order number KC12V3110 (quantity 3).
- Bracket and board alignment. The drive bracket must be correctly seated to the back plate, and the PC board correctly snapped onto the drive bracket.
- Piston and spacer stack. Foreign matter in the valve, or “high drive forces on piston,” means removing the drive cap and inspecting or replacing the piston and spacer stack.
The manual describes the valve as serviceable with hand-tightened caps and nuts, and offers a W100SM wrench (order number KC12V3193) but says “no tools are necessary to assemble or disassemble the valve.” Its warnings say not to use “a pipe wrench to tighten or loosen nuts or caps” or to put a screwdriver in the cap slots. Our Watts water softener parts guide lists the order numbers for the motor, board, pistons and spacer stack.
Watts’ warranty in the same manual excludes labor and freight, and requires a Return Goods Authorization for returns (WM100SM manual, PDF page 2). If the softener is under warranty, contact the dealer before replacing parts.
Other codes: contact the factory
The table ends: “If other Error Codes display contact the factory.” Elsewhere the manual says that if “ERROR” and a number alternately flash, you should “contact the OEM for help. This indicates that the valve was not able to function properly” (WM100SM manual, PDF page 12). The 2026 catalog lists Watts’ US number as (800) 659-8400.
Before calling, write down the code and check Valve History. The manual’s quick reference says pressing the down and up arrows, then down and up again, shows the software version, maximum flow rate, total gallons, total days, total regenerations and “number of error occurrences since start-up” (WM100SM manual, PDF page 10).
Display problems that are not error codes
The manual’s troubleshooting table covers several display faults (WM100SM manual, PDF pages 26 and 27):
| Problem | Causes the manual lists | Fix |
|---|---|---|
| Timer does not display time of day | Transformer unplugged, no power at outlet, defective transformer or PC board | Connect power, use a working outlet, replace transformer or board |
| Wrong time of day | Switched outlet, power outage, defective board | Use an uninterrupted outlet, reset the time |
| No “softening” display while water flows | Bypass in bypass position, stalled meter turbine, defective meter or board | Return bypass to service, clean or replace meter |
| Regenerates at the wrong time | Outage, clock or regeneration time wrong, valve set to “on 0” | Reset the time, check the regeneration time option |
| Time of day flashes | Power out more than two hours, transformer unplugged, valve reset | Reset the time of day |
The manual also says that if the power goes out for less than two hours, “the system will automatically reset itself,” and after a longer outage only the time of day needs resetting: “The system will remember the rest” (WM100SM manual, PDF page 12). The specifications list the board memory as “nonvolatile EEPROM.”
Stalls and regeneration faults without a code
Two more rows in the table describe regeneration problems that may not show an error (WM100SM manual, PDF page 27):
- Control valve stalled in regeneration: the motor is not operating, there is no power, or the transformer, board, drive gear, drive cap, piston retainer, or main or regenerant piston is broken.
- Regenerates when REGEN is pressed but not automatically: the bypass is in bypass, the meter is disconnected or stalled, the meter or board is defective, or there is a set-up error.
If water is hard but the display looks normal, see our Watts not-softening guide and the Watts regeneration guide.
Frequently asked questions
What does error 1002 mean on a Watts softener?
The WM100SM manual describes 1002 as “unexpected stall.” Start with the NEXT and REGEN reset for 3 seconds. If it returns, check the motor seating, drive gears, bracket and board alignment, and the piston and spacer stack for foreign matter.
How do I reset a Watts water softener?
Press NEXT and REGEN together for 3 seconds, or unplug the power jack (black wire) from the circuit board and plug it back in. The display flashes, shows the software version and returns the valve to service. Then reset the time of day.
What should I do if my Watts softener shows a code not listed?
The manual says to contact the factory for other error codes. Write down the code and the error count from the Valve History menu first. The 2026 Watts catalog lists (800) 659-8400.
Do these codes apply to Watts Locksmith softeners?
No. They come from the WM100SM manual for Watts’ W100-valve softeners. Locksmith systems use a different Watts controller, and we did not find a published Locksmith error list.