The short answer
On Bosch B freezers a compartment that is drifting up is usually losing cold rather than failing to make it: a seal that no longer grips, a vent packed with food, or an evaporator that defrost has stopped clearing. A freezer holds food safely at 0 F (-18 C) or below, and on the three models below that line decides how quickly you need to act rather than what the fault is.
What you observe on these models
- Temperature has drifted up over several days — Gradual warming is the defrost and airflow story rather than a sudden failure.
- Frost forms on packets rather than on the walls — Moist air getting in and freezing on the contents: a seal or a door problem.
- It was recently overfilled or restocked heavily — Packing against the vents stops circulation as effectively as a failed fan.
- The back of the cabinet is very hot and dusty — A condenser that cannot shed heat loses capacity, and clearing it is owner work.
- NEAR MISS - warm with water on the floor — Start on the leak page for the B family: the water usually explains the ice.
Causes, most likely first on the B family
- Defrost failure — First on the three models below where the interior carries a sheet of frost. Defrost runs on a schedule, and when it stops the ice closes the air path over days rather than hours.
- Airflow and how the compartment is packed — Second, and free to correct: a box against a vent does exactly what a failed fan does.
- Seals, hinges and doors left ajar — Third. Continuous ingress overloads the cabinet, and a drawer holding a door open a fraction is easy to miss for weeks.
- Condenser and the sealed system — Last, and the group where guessing is expensive. Clear the dust, give the cabinet clearance, and call.
Check in this order, and why
- First: rule out the free causes — Door closing fully, nothing packed against the vents, the cabinet not boxed in, the condenser clear of dust.
- Second: establish how it went warm — Over days points at defrost and ingress; all at once points at power or the compressor. That question reorders everything below it.
- Third: give any change a full day — A loaded compartment takes that long to settle, and judging after an hour produces a wrong conclusion.
- Fourth: stop at the interior panel — Defrost parts and fans on the B family sit behind it, and the sealed system is licensed work.
Before you open anything
Safety
Isolate the appliance before any panel comes off, and treat the sealed system as out of bounds; a capacitor can hold a charge after the power is off. If the compartment has been above 0 F (-18 C) for a long period, deal with the food first: refreezing thawed food is the risk here, not the appliance.
Models in the B family
Reference| Model number | Family key |
|---|---|
| B18IF800SP | bosch:freezer:b |
| B18IF900SP | bosch:freezer:b |
| B18IF905SP | bosch:freezer:b |
When to call a technician
Call once the seal, the vents, the packing and the condenser are all clear and a measured compartment is still above 0 F (-18 C). On the B family defrost parts and fans are behind the interior panel, and the sealed system is licensed work. Call immediately if the unit is silent and everything is thawing.
Sources — The symptom-report corpus recorded against Bosch B freezer pages for this fault is cited below. No share is quoted from it anywhere on this page: the snapshot reaches this page as a provenance chain without values, so every ordering here is technician judgement rather than a measured proportion.
Documented- amazon-reviews — amazon-reviews, fetched 2026-09-02
Other faults covered for the B family
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
