The short answer
A Bosch upright that runs constantly but will not hold temperature is usually iced up behind the rear wall. A full defrost that restores normal freezing proves it. Condenser dust and a door that no longer seals come next, and the sealed system is last.
What you observe
- Ice cream soft while the cabinet runs constantly — Long runs with a warm compartment mean air is not moving or heat is not leaving.
- A solid frost sheet on the rear wall inside — The airway is closing, which is the frost-free failure mode.
- The top drawer noticeably warmer than the bottom — Air is not circulating, so the cold settles where it is made.
- The back of the cabinet very hot — Heat that cannot leave the condenser returns to the room instead.
- NEAR MISS - warm for hours after a big shop — A full cabinet takes time to refreeze a warm load.
Causes, most likely first on this brand
- A defrost cycle that has fallen behind — First on this family by a wide margin. Once the evaporator ices over, the fan cannot move air across it, and the cabinet warms while the compressor runs continuously. A full defrost that fixes it, followed by frost returning in days, is the diagnosis.
- A stalled evaporator fan — Second. No air movement produces the same warm cabinet without the frost sheet to explain it, and the top of the compartment suffers first.
- A condenser that cannot reject heat — Third. Dust on the coil, or a tall cabinet pushed hard against a wall in a warm utility room, means the compressor runs longer and longer for less cooling.
- A door that does not close or seal — Fourth. Upright freezer doors are heavy and the seal is worked hard; a continuous ribbon of humid air both warms the cabinet and feeds the ice that causes the first item here.
- A sealed-system or compressor fault — Last, and the only one that is not an owner check. Reached by elimination.
Check in this order, and why
- Look at the rear wall inside for a frost sheet — It answers the airflow question immediately and without tools.
- Listen for the evaporator fan with the door held shut — Most door switches cut the fan, so use the switch rather than your eyes.
- Inspect and vacuum the condenser — Hot is expected; furred with dust or jammed against a wall is not.
- Test the door seal with a sheet of paper all round — A tall door usually fails at one end rather than everywhere.
What an owner can safely check
- Move the contents to a cool box or a neighbour's freezer — A freezer holds food safely at 0 degrees Fahrenheit or below; judge by that rather than by how long it has been warm.
Tools: cool boxAbout 30 min
- Defrost the cabinet completely with the door open — Let every trace of ice melt, then dry the interior before restarting.
Tools: towelsAbout 120 min
- Vacuum the condenser and restore the air gap — Clean the coil, clear the plinth vent and pull the cabinet clear of the wall.
Tools: vacuum, soft brushAbout 30 min
- Test the seal and the self-closing action — Set the front feet slightly higher than the back so the door swings shut on its own.
Tools: paper, adjustable wrenchAbout 25 min
- STOP HERE if freezing does not return after a full defrost — That diagnosis needs gauges rather than hands.
Before you open anything
Safety
Unplug the freezer before removing any panel - a capacitor can hold a charge after the power is off, and the defrost heater sits directly behind the rear interior panel. Never speed a defrost with a heat gun or a hair dryer against the liner, and never chip at ice with a metal tool, because a punctured evaporator ends the appliance. Get help before moving a tall cabinet, which tips forward once the door is open.
When to call a technician
Call when a full defrost restores freezing and the frost returns within a week or two, because that is a defrost heater, sensor or control rather than a one-off. Call as well when the cabinet stays warm with a clean condenser and a running compressor, which is the sealed system and is licensed work. Call immediately if you smell burning or see oil near the compressor.
Nearest pages of this class
What this page does not cover
This page covers the Bosch upright and column freezers as a class, not one model family; a family-specific page is more precise where one exists. Not included here: defrost heater and sensor part identifiers, temperature set points, refrigerant charge and clearance dimensions, all of which differ between the built-in, freestanding and counter-depth families.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
