Bosch Dryer Error E18 — What It Means & How to Fix It

What Does This Error Mean?

E18 on a Bosch heat pump dryer means the compressor or heat pump inverter board has a fault. The heat pump compressor is the core component that generates heat — when it fails or its control board faults, E18 appears and the dryer cannot produce heat. This is a serious fault that almost always requires a technician.

Affected Models

Bosch WTH84000GB
Bosch WQB145B0GB
Bosch WTW87565GB
Bosch Serie 8 Heat Pump Dryer
Bosch Serie 6 Heat Pump Dryer (WTH series)

Common Causes

Heat pump compressor failed — the compressor motor or its refrigerant circuit has developed a fault
Inverter board (compressor control board) fault — the board driving the compressor has failed
Refrigerant pressure too low — refrigerant has leaked from the sealed heat pump circuit
Compressor overheating due to restricted airflow — caused by a blocked filter or heat exchanger
Power supply issue causing voltage fluctuations that damage the inverter board

How to Fix It

Unplug the dryer and wait 10 minutes, then restart.

Compressor inverters can occasionally fault due to transient electrical events. A 10-minute power drain sometimes clears the error. If E18 returns, the fault is genuine.
Clean the lint filter and heat exchanger fluff filter thoroughly before calling for service.

A blocked filter can cause the compressor to overheat, triggering E18. Cleaning these before the technician visit rules out the simplest cause and may even resolve the fault.
Check the dryer is in a room with a temperature between 5 and 35 degrees C.

Heat pump dryers cannot operate correctly outside this temperature range. Very cold garages or laundry rooms can prevent the heat pump from functioning and trigger E18.
If E18 persists, do not attempt further resets — call Bosch service.

Repeatedly restarting with a faulty compressor can cause further damage to the inverter board.

When to Call a Professional

E18 almost always requires a Bosch authorised engineer. The heat pump refrigerant circuit and inverter board are specialist components. Refrigerant work legally requires a qualified F-Gas certified technician in the UK and EU. Contact Bosch on 0344 892 8979 (UK) to book a service visit.

Frequently Asked Questions

Is it worth repairing a Bosch heat pump dryer with E18?

It depends on the dryer's age. Heat pump compressors are expensive to replace — typically £300–600 for the part plus labour. For a dryer under 4 years old, repair is usually worthwhile. For a dryer over 7–8 years old, a new machine may be more economical. Get a repair quote before deciding — Bosch engineers can often repair the inverter board for less than a full compressor replacement.

Does Bosch warrant the heat pump compressor?

Bosch's standard warranty is 2 years in the UK and EU. Some models sold with extended warranties cover the heat pump compressor for longer. Check your purchase documents or call Bosch with your model and serial number to confirm warranty coverage.