Direct answer: HALO publishes very few error codes, and they differ by product. On a HALO 5, the installation manual and quick-reference guide name two codes, E1 and E2, and give one fix: hold the SET button and an arrow button until you hear the gear recenter. On a CK10 softener or Hybrid, the manuals say that if “ERROR” and a number flash alternately, the valve “was not able to function properly” and you should “contact the OEM for help.” On a HALO UV system, a red light and audible alarm mean the unit “needs immediate attention.” HALO does not publish a table of what each CK10 error number means.
Publisher boundary: Water System Guide is an independent research publisher, not a HALO dealer. This page uses HALO’s HALO 5 installation manual (Rev.3326), HALO 5 quick-reference guide, CK10 manual (November 20, 2024), Hybrid manual (January 7, 2026) and UV spec sheet (November 13, 2025), reviewed October 15, 2026. We report only the codes and actions HALO prints. We do not invent meanings for error numbers HALO does not define.
First, identify which HALO controller you have
HALO’s error displays depend on which product you own:
- HALO 5 (H5-100 to H5-200). The quick-reference guide describes a controller with a SET button and up and down arrows, a time-of-day display and settings such as P7 (HALO 5 quick-reference guide). There is no brine tank.
- CK10 (H-CK10-150, 200, 250) and Hybrid. These manuals describe a valve with NEXT, REGEN, SET CLOCK and arrow buttons, and screens for diagnostics and valve history (CK10 manual, PDF page 14). They use a brine tank.
- ION 2.0 Plus. No power, no display, no codes.
- HALO UV. An LED indicator and audible alarm instead of codes.
If you are not sure which you have, our HALO 5 vs CK10 vs Hybrid comparison shows the differences.
HALO 5: E1 and E2
Both the quick-reference guide and the installation manual give the same instruction: “If the screen displays an E1 or E2 error code, hold set and [arrow] buttons until you hear the gear recenter, then release buttons” (HALO 5 installation manual, PDF page 7). The arrow symbol does not survive in the PDF text, so check the printed guide on your unit for which arrow to use.
The installation manual adds one more step: “If you press and hold the set and [arrow] and don’t hear the motor move, try disconnecting the motor and reinserting it. The motor’s inability to rotate could mean it’s out of alignment.”
What this tells you about E1 and E2:
- They relate to the drive gear and motor position. HALO’s fix is to recenter the gear, and the fallback is reseating the motor.
- HALO does not separate E1 from E2. Both get the same instruction.
- HALO does not say what to do if recentering does not clear the code. Its warranty sets the rule for that: put the system on bypass and contact HALO with the model number, serial number and photos before any parts are replaced (HALO 5 warranty).
After clearing E1 or E2
Once the code clears, check that the controller settings survived:
- Time of day. Hold SET for 5 seconds and set the hour, then the minutes. The quick-reference guide notes the hour is AM unless the PM indicator shows.
- Days between regeneration. HALO’s recommendation is 11 days for one person, 9 days for two to three, and 7 days for four or more, “unless otherwise requested by homeowner.”
- P7. The guide says P7 should show 99 with a blinking arrow next to days to regen. “If you see the number 7 instead of 99” it should be changed back to 99.
The quick-reference guide also says that after start-up it is “essential” to force 2 regenerations and flush every fixture for 2 minutes, because otherwise the customer “will likely complain about water quality and gray water.” If E1 or E2 appeared after a new installation, ask the installer whether those forced regenerations were done. Our HALO regeneration guide covers the HALO 5 cycle and how to start one.
CK10 and Hybrid: a flashing “ERROR” and number
The CK10 manual’s only error instruction reads: “If the word ‘ERROR’ and a number are alternately flashing on the display contact the OEM for help. This indicates that the valve was not able to function properly” (CK10 manual, PDF page 15). The Hybrid manual repeats the same wording (Hybrid manual, PDF page 15).
Neither manual lists what the numbers mean. The “OEM” for a HALO-branded system is HALO itself: the warranty directs owners to call (800) 591-0538 or email [email protected].
What to record before you call
The CK10 manual includes two read-only menus that give HALO or a technician useful history:
- Diagnostics. Press Down and Up together for three seconds to see days since the last regeneration, gallons since the last regeneration (zero if no meter is installed), and reserve capacity used in each of the last seven days (CK10 manual, PDF page 16).
- Valve History. The steps show software version, maximum flow since start-up, total gallons, total days, total regenerations, and an Error Log that “shows a history of the last 10 errors generated by the control during operation” (CK10 manual, PDF page 17). The manual notes these values “cannot be reset.”
If a diagnostic screen does not appear within 5 seconds, the manual says the valve lock is on, and gives the unlock sequence: Down, NEXT, Up and SET CLOCK in order, then the menu’s button combination again.
Write down the error number, the error log entries, the software version and the total regenerations. Together with photos of the valve and brine tank, that is what HALO’s warranty process asks a technician to collect before replacing anything.
CK10 and Hybrid: a flashing time of day
A flashing clock is not an error code, but owners often mistake it for one. The CK10 manual explains the two cases (CK10 manual, PDF page 15):
- After an outage longer than 8 hours, the time of day flashes “which indicates the time of day should be reset. The system will remember the rest.”
- If the clock flashes after an outage shorter than 8 hours, “the non rechargeable battery should be replaced.”
The same manual’s valve description, on an earlier page, says “the control valve does not need batteries” and keeps settings for two hours (CK10 manual, PDF page 5). The two passages disagree. If your clock keeps flashing after short outages, ask HALO or your installer whether your valve has a replaceable battery before buying one.
A wrong clock matters because the CK10 regenerates at a set time, 2:00 a.m. by default. If the time is off, regeneration can run while the household is using water, and the manual warns that “if there is a demand for water when the system is regenerating, untreated water will be used.”
HALO UV: red light and alarm
The UV spec sheet describes a monitoring system with one LED that shows two colors. “GREEN indicates that the UV lamp is satisfactory and the unit is in good working order. RED indicates that the unit needs immediate attention, the audible alarm will sound when the LED monitor light switches to red.” It adds: “If the lamp has been in service for a year or more, it should be replaced” (HALO UV spec sheet).
The spec sheet’s parts list gives H-UV12-LAMP-HD as the replacement bulb and H-UV12-SLEEVE-HD as the quartz sleeve, with a schedule of one lamp a year and a sleeve every 3 years. Because UV only treats water when the lamp is working, a red light is the one HALO warning that affects disinfection, not just convenience. See our HALO parts guide for the full list.
Problems that are not error codes
Most HALO complaints do not show a code at all. HALO’s documents point to these causes:
| Symptom | Product | What HALO’s documents say |
|---|---|---|
| Gray or cloudy water after installation | HALO 5 | Force 2 regenerations and flush each fixture for 2 minutes; repeat if still cloudy |
| Carbon fines at fixtures | HALO 5 | Clean carbon residue from fixtures after the forced regenerations |
| Hard water still present | HALO 5 | HALO 5 conditions, it does not soften; see our not-softening guide |
| Hard water after a softener regeneration | CK10 | Manual: if the brine tank had no salt, add salt and “wait at least two hours before regenerating” |
| Regeneration at the wrong time | CK10 | Reset the clock; check the regeneration hour in the installer settings |
If hardness is the problem, our HALO not-softening guide works through the checks for each product.
When to stop and call HALO
HALO’s warranties put limits on owner repairs. The HALO 5 warranty says the system “must be maintained with HALO approved replacement components,” that “the customer must contact the HALO representative prior to any repairs or replacements,” and that HALO “does not warrant to perform, pay for, or finance any repairs and/or installations.” Call HALO or your installer, with the system on bypass, if:
- E1 or E2 returns after recentering and reseating the motor.
- “ERROR” and a number flash on a CK10 or Hybrid.
- Water leaks from the valve, tank or drain line.
- The UV light stays red after a lamp change.
Frequently asked questions
What does E1 or E2 mean on a HALO 5?
HALO does not define them separately. Its guides give one fix for both: hold SET and the arrow button until you hear the gear recenter. If the motor does not move, the manual says to disconnect and reinsert the motor, since it may be out of alignment.
What do the CK10 error numbers mean?
HALO does not publish a list. The CK10 and Hybrid manuals say a flashing “ERROR” and number means the valve could not function properly and you should contact the OEM. The Valve History menu stores the last 10 errors for a technician.
Why is the clock flashing on my HALO CK10?
The manual says the clock flashes after a power outage longer than 8 hours and only the time needs resetting. If it flashes after a shorter outage, the manual says to replace the non-rechargeable battery, though another page says the valve needs no batteries.
What does a red light on a HALO UV system mean?
The spec sheet says red, with an audible alarm, means the unit needs immediate attention. It also says a lamp in service for a year or more should be replaced, and lists the lamp as H-UV12-LAMP-HD.