Loretto Cold Service — (904) 664-4866 — independent Sub-Zero refrigeration service in Mandarin, Jacksonville, FL.
Booking: (904) 664-4866 (tel:+19046644866). Source: https://duvalsubzero.com/porch-notes/hollow-ice-cubes/

# Why Ice Cubes Come Out Hollow

> Hollow or thin cubes usually mean the fill valve is metering short, not that the freezer is warm. How to tell the two apart, and what the repair involves.

Topic: ice and water. Published 2026-08-10.

A hollow cube looks like a freezing problem. It is almost never a freezing
problem.

Here is the sequence an ice maker actually runs. The fill valve opens for a
fixed number of seconds and lets water into the mould. The mould sits there
while the freezer does its ordinary work. At the end of the cycle the mould is
warmed slightly, the bond breaks, and the cubes are swept out into the bin. Then
it starts again.

Notice what is missing from that description: at no point does the machine check
whether the mould actually filled. The timing is fixed. The machine assumes the
valve delivered what it was asked for.

## Why a short fill produces a shell

Water freezes from the outside in. A full mould freezes into a solid cube
because there is water all the way through. A mould that only received two
thirds of its shot freezes a shell first, and there is nothing left in the
middle to fill it. When the harvest cycle sweeps it out, you get a cube that is
the right shape and the wrong weight, and often one that collapses in a glass.

If the cabinet were genuinely too warm, you would not get hollow cubes. You
would get soft ones, or slushy ones, or none at all — and the ice cream two
shelves down would be telling you the same story. Check the food before you
blame the temperature. Firm food plus poor ice is a water problem, every time.

## Where short fills come from

In rough order of how often we find them:

**Mineral deposit on the valve seat.** Every fill leaves a trace behind on the
seat the water passes through. Over years the passage narrows, the same number
of seconds delivers less water, and the cube gets progressively lighter. This is
the slow, gradual version, and it is the one we find most often.

**A restricted supply line.** The line feeding the refrigerator is often
original to the last kitchen remodel. Twenty-five years of the same water has
the same effect on a quarter-inch line that it has on a valve seat, and a kinked
or partly crushed line behind a cabinet does it faster.

**A failing valve.** Solenoid valves do eventually fail, and when they do it is
usually more sudden — cubes were normal, then they were not.

**Low household pressure at the moment of fill.** Less common, but real if
something else in the house draws hard at the same time.

## Two things to notice before you call

**Did it arrive gradually or suddenly?** A gradual decline over a season or two
points at deposit, in the valve or the line. A change you can date to a particular
week points at the valve, the line being disturbed, or something that happened
to the plumbing.

**Has anything else that meters water slowed down?** If a bathroom fixture or
another appliance changed at the same time, the problem is upstream of the
refrigerator entirely and the ice maker is just the most sensitive instrument
in the house.

## What the repair looks like

We measure the actual fill volume rather than inferring it, check pressure at
the appliance, inspect the valve and the line, and look at the mould surface.
Replacing a valve that is being fed by a restricted line is a repair that lasts
about eighteen months, so the line gets checked either way.

Sometimes the answer is a part. Sometimes the answer is that the line needs
replacing and the valve is fine. Occasionally the answer is that the machine is
healthy and the household is simply asking more of it in August than it did in
February, in which case you have bought a straight answer and not a part you did
not need.

The diagnostic is a flat $129 and comes off the repair if you go ahead.

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Loretto Cold Service is an independent appliance repair company. We are not affiliated with, authorized by, or endorsed by Sub-Zero or its parent company. All brand names and model numbers are the property of their respective owners and are used only to identify the appliances we service.

Loretto Cold Service · (904) 664-4866 · Mandarin, Jacksonville, FL