Bosch Refrigerator Error E27 — How to Fix

What Does This Error Mean?

Bosch fridge E27 means the compressor cannot start or is not running correctly. Before assuming the compressor has failed, test the start relay — a small plug-in component on the compressor side that costs around $15 and fails regularly. Shake the start relay next to your ear — if it rattles, the relay is broken and needs replacing.

Affected Models

Bosch Series 2 Fridge-Freezer
Bosch Series 4 Fridge-Freezer
Bosch Series 6 Fridge-Freezer
Bosch KGN Series
Bosch KGV Series

Common Causes

Start relay failed — this small component initiates the compressor motor and commonly fails without warning
Compressor motor winding has failed — requires professional diagnosis and refrigerant handling
Compressor overloaded by high ambient temperature or a blocked condenser, triggering the thermal overload
Wiring between the control board and compressor is damaged or a connector has corroded
Control board relay switching power to the compressor has failed

How to Fix It

Locate the start relay

Pull the fridge from the wall and remove the lower back panel. The compressor is a large dome-shaped unit. The start relay is a small rectangular or round plug attached to pins on the side of the compressor.
Test the start relay

Pull the start relay straight off the compressor pins. Shake it next to your ear — if you hear rattling, the internal capacitor has broken and the relay is faulty. Even without rattling, a relay over 5 years old is worth replacing.
Replace the start relay

Order a replacement start relay matching your compressor model (the model number is printed on a label on the compressor body). The relay simply plugs back onto the same pins. Cost is $10–20. This is the most common fix for E27.
Check condenser for blockages

A heavily blocked condenser causes the compressor to overheat, triggering its thermal overload and showing as E27. Vacuum the condenser coils at the back of the fridge and ensure at least 10 cm of clearance behind the unit.
Allow the compressor to cool

If the compressor tripped its thermal overload, it will not restart until it cools. Turn the fridge off for 2–3 hours, then switch it back on. If E27 clears and the fridge cools normally, the thermal overload was the cause.

When to Call a Professional

If the start relay is intact but E27 continues, the compressor motor itself has failed. Compressor replacement requires refrigerant recovery — this must be done by a certified technician. Contact Bosch service.

Frequently Asked Questions

How do I know if the compressor has failed or just the start relay?

Remove the start relay and shake it — if it rattles, replace it. If the relay is intact and the compressor still does not run after replacement, the compressor motor itself has failed and a technician is needed.

Bosch fridge making a clicking sound and not cooling — is that E27?

A clicking sound every 2–5 minutes with no cooling is the classic symptom of a failed start relay. The compressor tries to start, the relay fails, trips, resets, and tries again. Replace the start relay first — it is a $15 fix.

How urgent is Bosch fridge E27?

Very urgent — with E27 active, the fridge is not cooling. Food will spoil within 4–6 hours. Move food to a temporary cooler while you diagnose and repair E27.