Sub-Zero error code · 40 8 40
Sub-Zero Code 40 8 40: Icemaker Maximum Fill Time Exceeded
Sub-Zero code 40 8 40 means the icemaker ran its full fill cycle without reaching the needed water volume. Usual cause: low water pressure, kinked line, or.
Sub-Zero code 40 8 40 means the icemaker ran for its maximum allowed fill time but never reached the required water volume, so the fill timed out. The usual fix is restoring proper water flow by clearing a kinked or frozen supply line, replacing a clogged water valve, or correcting low household water pressure.
40 8 40, explained
The control board opens the icemaker water valve for a fixed maximum fill duration. When that time elapses and the icemaker has still not received enough water to complete a harvest, the board logs 40 8 40. It points to a water-delivery problem on the icemaker fill circuit rather than a board failure, and it typically results in undersized or empty ice cubes.
Severity:Service recommended
How 40 8 40 shows up
- Ice cubes are hollow, undersized, or partially formed
- Icemaker bin runs empty and does not refill
- Audible water valve buzz with little or no water reaching the mold
- Long delays between ice harvests
- Recurring fill faults logged after a new filter or shutoff adjustment
What usually causes it
- Low household or supply-line water pressure below unit minimum
- Kinked, crimped, or partially frozen inlet water line
- Clogged or scaled icemaker water valve restricting flow
- Saddle valve or shutoff not fully open
- Severely restricted water filter or overloaded RO system
Which part 40 8 40 points to
- Icemaker water inlet valve — Replaced when the solenoid is clogged, scaled, or fails to pass full rated flow
- Water supply line / tubing — Replaced if kinked, crimped, or damaged and restricting flow
- Water filter cartridge — Replaced if a clogged filter is starving the fill circuit
Why 40 8 40 appears
Most often the household water pressure is below the unit's minimum, the saddle valve or shutoff is partly closed, or the inlet line is kinked or partially frozen. The icemaker water valve solenoid can also clog with mineral scale or weaken with age so it does not pass full flow, and a heavily loaded RO or filter system can starve the line.
What you can safely check
- Confirm the household water shutoff and saddle valve are fully open
- Inspect the visible supply line behind the unit for kinks or sharp bends
- Replace an old water filter cartridge and confirm dispenser water flows freely
- Note the code and how often it recurs, then power-cycle the unit at the breaker
When 40 8 40 needs a technician
A technician is needed to measure actual water pressure and flow, test the inlet valve solenoid, and inspect for frozen or restricted tubing inside the cabinet that an owner cannot safely access.
Got 40 8 40?
We'll pinpoint it and bring the right part. $89 diagnostic, 365-day warranty.
Book a technicianHow to enter service mode →All Sub-Zero error codesAll brands
Frequently asked
Sub-Zero 40 8 40 — questions
What does Sub-Zero code 40 8 40 actually mean?
Code 40 8 40 means the icemaker opened its water valve for the maximum allowed fill time but never received enough water to complete a harvest, so the fill timed out. It is a water-delivery problem on the icemaker fill circuit, not a control-board failure, and it usually shows up as hollow, undersized, or partly formed ice cubes.
Are there things I can safely check myself before calling for 40 8 40?
Yes, several. Confirm the household water shutoff and saddle valve are fully open, inspect the visible supply line behind the unit for kinks or sharp bends, replace an old water filter cartridge and verify the dispenser water flows freely, then note how often the code recurs. These owner checks address the most common causes of a fill timeout.
How do I clear code 40 8 40 once I've fixed the water flow?
After restoring proper water flow, power-cycle the unit at the breaker and let the icemaker run a full cycle. If flow is genuinely restored, 40 8 40 should not return; if it logs again, the inlet valve may be scaled or the pressure is still below the unit's minimum and needs a technician's measurement.
Is it harmful to keep using the refrigerator with a 40 8 40 fault?
It is a medium-severity, ice-only issue, so the refrigerator and freezer keep cooling normally and the food is not at risk. The practical downside is little or no ice, plus an icemaker water valve that may keep buzzing while trying to fill. It is fine to keep using the unit, but a starved valve left running is worth resolving.
Which part is usually replaced for 40 8 40 and what does service cost?
The common parts are the icemaker water inlet valve when it is clogged or scaled, a kinked supply line, or a severely restricted water filter. We measure actual pressure and flow and test the solenoid for a flat $89 diagnostic, back the repair with a 365-day warranty, and take calls at (650) 668-1554.
How is 40 8 40 different from the dispenser run-time code 40 9 40?
They sound alike but are opposite problems. 40 8 40 is a fill timeout where too little water reaches the icemaker mold, pointing to pressure, a kink, or a clogged valve. 40 9 40 is a dispenser run-time limit where water flows too long, usually from a stuck dispenser pad. One is about not enough water at the icemaker, the other about water that won't stop at the dispenser.
Subzero Repair · Open 24/7 · 365-day warranty
Need a high-end appliance repaired?
Call for urgent cooling or cooking failures, or book online for a service window across the Bay Area.