Why does my freezer ice up?

Frost does not come from the freezer. It comes from water vapour in room air that enters the cabinet and freezes onto the first cold surface it meets, and from moisture evaporating off food that is not properly wrapped. That means the diagnosis is always the same shape: find how the moisture is getting in, or find why the appliance has stopped removing it.

Safety

What you'll need

• A sheet of paper, for the seal test
• A freezer thermometer
• A plastic scraper
• Towels and warm water
• A hairdryer on a low setting (optional)

Step by step

1. Work out whether your freezer is static or frost free.A static freezer has cold shelves and frost forms all over the interior. A frost free one has a rear panel with vents and a fan, and should never accumulate visible ice. The distinction decides which of the causes below apply.
2. Test the door seal with a piece of paper.Close the door on a sheet of paper and pull. It should grip. Do it every 100mm around all four sides and both hinge and handle edges. A section that lets the paper slide out freely is drawing in humid room air continuously, and that is the commonest cause of heavy icing.
3. Check the door actually closes and the appliance is level.An overfilled drawer, a bag sticking out, or a freezer tilted forward all leave the door a few millimetres off its seal. That is enough. Most appliances should sit very slightly tilted back so the doors self-close under their own weight — check with a spirit level and adjust the front feet.
4. Look at where the ice actually is.Ice heaviest around the door opening points at the seal or the door. Ice on one shelf points at a warm or wet item on it. Ice on the rear panel of a frost free freezer points at the defrost system. Ice in the base points at a blocked drain. The location is the diagnosis.
5. Check your habits with warm and uncovered food.Warm food carries a lot of moisture and releases it into the cabinet. Uncovered food, half-open bags and open ice cream tubs give up moisture continuously. Cool food to room temperature first, and wrap everything properly with the air pressed out.
6. Check how often and how long the door is open.Standing with the door open deciding what to eat is one of the largest single sources of frost. So is a door not fully latched overnight, which is the classic cause of finding a heavily iced freezer one morning.
7. On a frost free freezer, find and clear the defrost drain.There is a small drain hole at the base of the evaporator compartment behind the rear panel, taking meltwater out to a tray on the compressor. When it blocks or freezes, meltwater backs up and forms a slab of ice in the base. Fully defrost the appliance and flush the drain with warm water.
8. Suspect the defrost system if a frost free freezer ices up repeatedly.A failed defrost heater, thermostat or timer means the evaporator never gets cleared, so it ices solid, airflow stops and the cabinet warms while the compressor runs constantly. It is an engineer's diagnosis and a repairable one.
9. Defrost it fully once, then watch how fast the ice returns.This is the diagnostic as much as the cure. Ice back within weeks means an active cause you have not found. Ice back over a year in a static freezer is entirely normal.
10. Consider replacing the door seal if the paper test failed.A seal is one of the cheapest parts on the appliance and one of the most worthwhile to replace. Most are push-in or screw-retained and it is genuinely an owner job on many models.

Common mistakes

• Attacking the ice with a knife or a screwdriver — The refrigerant pipework runs directly behind the liner. Puncturing it vents the gas, scraps the appliance, and releases flammable isobutane into the kitchen on almost every modern model.
• Defrosting repeatedly without finding the cause — Heavy ice returning within weeks means air or moisture is getting in, or the defrost system has failed. Defrosting treats the symptom and hides the fault while the appliance runs inefficiently all year.

If it doesn't work

Questions people ask