The short answer
A Bosch B refrigerator that is warm in one compartment and cold in the other has an airflow fault, not a refrigeration fault. On the models below the two compartments share one cold source, so a blocked path or an evaporator that has iced over starves one side while the other stays fine. The sealed system is the last thing to suspect, not the first.
What you observe on these models
- The fresh-food side is warm while the freezer is still cold — The single most diagnostic observation available: one cold source, one blocked path.
- The unit runs almost continuously — It is trying and not getting there, which fits airflow and defrost rather than a failed compressor.
- A sheet of frost on the freezer rear wall — Not the usual light dusting: a solid sheet means defrost has stopped clearing it.
- Food in the door is warmer than food at the back — Normal to a degree, but pronounced when circulation has stopped.
- NEAR MISS - the cabinet is silent and nothing is cold — That is power, a start relay or a compressor, and it presents completely differently.
Causes, most likely first on the B family
- Doors, seals and ingress — First on the B family because it is free, common and invisible: a seal that no longer grips or a door held a fraction open by a drawer will warm a cabinet with nothing broken anywhere.
- Airflow inside the cabinet — Second. Vents blocked by food, a fan that has stopped, or an evaporator icing over all starve one compartment while the other stays cold.
- Defrost — Third in rank and usually the underlying cause when frost is visible: ice on the rear wall is what airflow is being blocked by.
- Condenser, fans and refrigerant — Last. Clean the condenser and make sure the unit is not boxed in; beyond that it is a service call, and one where guessing is expensive.
Check in this order, and why
- First: establish how it went warm — Over days points at defrost and airflow; all at once points at power, a door, or the compressor. That single question reorders everything below it.
- Second: listen — A running unit that is not cooling is a different fault from a silent one. Silence with a warm cabinet means power, a relay or a compressor.
- Third: clear the condenser and the surroundings — Dust on the coil and no clearance around the cabinet both reduce capacity, and both are owner work.
- Fourth: stop at the rear panel — Defrost components, fans and the sealed system on the B family sit behind it, and refrigerant work 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: refrigerant work is licensed work and the tools for it are not owner tools. A capacitor can hold a charge after the power is off. If food has been above 40 F (4 C) for hours, deal with the food before dealing with the appliance.
Models in the B family
Reference| Model number | Family key |
|---|---|
| B09IB80NSP | bosch:refrigerator:b |
| B09IB81NSP | bosch:refrigerator:b |
| B09IB91NS* | bosch:refrigerator:b |
| B10CB80NV* | bosch:refrigerator:b |
| B10CB81NV* | bosch:refrigerator:b |
| B11CB50SSS | bosch:refrigerator:b |
| B11CB81SSS | bosch:refrigerator:b |
| B18ID80*** | bosch:refrigerator:b |
| B18IF800SP | bosch:refrigerator:b |
| B18IF900SP | bosch:refrigerator:b |
| B18IF905SP | bosch:refrigerator:b |
| B20CS30SNS | bosch:refrigerator:b |
| B20CS50SNB | bosch:refrigerator:b |
| B20CS50SNI | bosch:refrigerator:b |
| B20CS50SNS | bosch:refrigerator:b |
| B20CS50SNW | bosch:refrigerator:b |
| B20CS51SNB | bosch:refrigerator:b |
| B20CS51SNI | bosch:refrigerator:b |
| B20CS51SNS | bosch:refrigerator:b |
| B20CS51SNW | bosch:refrigerator:b |
| B20CS80SNB | bosch:refrigerator:b |
| B20CS80SNS | bosch:refrigerator:b |
| B20CS80SNW | bosch:refrigerator:b |
| B20CS81SNB | bosch:refrigerator:b |
| B20CS81SNS | bosch:refrigerator:b |
| B20CS81SNW | bosch:refrigerator:b |
| B21CL80SNS | bosch:refrigerator:b |
| B21CL81SNS | bosch:refrigerator:b |
| B21CT80*** | bosch:refrigerator:b |
| B21CT80SNS | bosch:refrigerator:b |
| B22CS30SNS | bosch:refrigerator:b |
| B22CS50SNS | bosch:refrigerator:b |
| B22CS50SNW | bosch:refrigerator:b |
| B22CS51SNS | bosch:refrigerator:b |
| B22CS80SNS | bosch:refrigerator:b |
| B22CS81SNS | bosch:refrigerator:b |
| B22CT80SN* | bosch:refrigerator:b |
| B22FT80SNS* | bosch:refrigerator:b |
| B24CB50ES* | bosch:refrigerator:b |
| B24CB50ESS | bosch:refrigerator:b |
| B24CB80ES* | bosch:refrigerator:b |
| B24CB80ESS | bosch:refrigerator:b |
| B24ID80*** | bosch:refrigerator:b |
| B24IF70*** | bosch:refrigerator:b |
| B26FT**SN* | bosch:refrigerator:b |
| B26FT50SNS | bosch:refrigerator:b |
| B26FT70SNS | bosch:refrigerator:b |
| B26FT80SNS | bosch:refrigerator:b |
| B26FT81SNS | bosch:refrigerator:b |
| B30BB130S* | bosch:refrigerator:b |
| B30BB130SS | bosch:refrigerator:b |
| B30BB830** | bosch:refrigerator:b |
| B30BB830SS | bosch:refrigerator:b |
| B30BB930SS | bosch:refrigerator:b |
| B30BB935SP | bosch:refrigerator:b |
| B30BB935SS | bosch:refrigerator:b |
| B30IB100S* | bosch:refrigerator:b |
| B30IB100SP | bosch:refrigerator:b |
| B30IB800SP | bosch:refrigerator:b |
| B30IB900SP | bosch:refrigerator:b |
| B30IB905SP | bosch:refrigerator:b |
| B30IB910SP | bosch:refrigerator:b |
| B30IR800SP | bosch:refrigerator:b |
| B30IR900SP | bosch:refrigerator:b |
| B30IR905SP | bosch:refrigerator:b |
| B33CM10SNS | bosch:refrigerator:b |
| B36BT130N* | bosch:refrigerator:b |
| B36BT130NS | bosch:refrigerator:b |
| B36BT830NS | bosch:refrigerator:b |
| B36BT930NS | bosch:refrigerator:b |
| B36BT935NS | bosch:refrigerator:b |
| B36CD10EN* | bosch:refrigerator:b |
| B36CD30EN* | bosch:refrigerator:b |
| B36CD50SN* | bosch:refrigerator:b |
| B36CD51SN* | bosch:refrigerator:b |
| B36CD52SN* | bosch:refrigerator:b |
| B36CD80EN* | bosch:refrigerator:b |
| B36CD80SN* | bosch:refrigerator:b |
| B36CL80*NS | bosch:refrigerator:b |
| B36CL80EN* | bosch:refrigerator:b |
| B36CL80SN* | bosch:refrigerator:b |
| B36CL81EN* | bosch:refrigerator:b |
| B36CL84ENG | bosch:refrigerator:b |
| B36CL84ENS | bosch:refrigerator:b |
| B36CL84ENW | bosch:refrigerator:b |
| B36CL84SN* | bosch:refrigerator:b |
| B36CT80SN* | bosch:refrigerator:b |
| B36CT81EN* | bosch:refrigerator:b |
| B36CT81SN* | bosch:refrigerator:b |
| B36CT82EN* | bosch:refrigerator:b |
| B36CT82SN* | bosch:refrigerator:b |
| B36CT84EN* | bosch:refrigerator:b |
| B36CT84SN* | bosch:refrigerator:b |
| B36ET71S** | bosch:refrigerator:b |
| B36FD10EN* | bosch:refrigerator:b |
| B36FD30EN* | bosch:refrigerator:b |
| B36FD31EN* | bosch:refrigerator:b |
| B36FD50SN* | bosch:refrigerator:b |
| B36FD51SN* | bosch:refrigerator:b |
| B36FD52SN* | bosch:refrigerator:b |
| B36FD54SN* | bosch:refrigerator:b |
| B36IT100N* | bosch:refrigerator:b |
| B36IT100NP | bosch:refrigerator:b |
| B36IT71*** | bosch:refrigerator:b |
| B36IT800NP | bosch:refrigerator:b |
| B36IT900NP | bosch:refrigerator:b |
| B36IT905NP | bosch:refrigerator:b |
| B36IT930NP | bosch:refrigerator:b |
When to call a technician
Call once the seals, the vents, the condenser and the packing are all clear and a measured compartment is still above what food safety needs. On the B family defrost components and fans sit behind a rear panel, and the sealed system is licensed work. Call immediately if the unit is silent and warm, because that is power or compressor rather than airflow.
Sources — The symptom-report corpus recorded against Bosch B refrigerator 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
SC
Sarah Chen
Lead Appliance Repair Technician · 12 years experience
EPA 608 UniversalNASTeC Certified
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
