WMF Automatic Coffee Machine Error Code 188: Heater Error

What does WMF error code 188 mean?

The heater heats the machine's water, and the control monitors it through temperature readings and a safety cut-out. Code 188 appears when the control sees a problem with the heating, and drinks stop. The heater element and its wiring carry mains power, which is why the owner's manual tells the user to switch off, disconnect the plug and call service instead of trying to restart repeatedly. A failed element or damaged wiring, a switch or safety cut-out that opens too early, a temperature sensor that misreads the water heat, or a power supply problem to the heater circuit can each lead to the same code. The display cannot tell them apart, and the correct response is the same for all of them. Running a machine with a heater problem could heat water uncontrolled or not at all, so the safe choice is to leave it unplugged.

Affected models and control systems

This applies to the WMF 5000 S+ and to the WMF 1500 F with internal storage, per the WMF 5000 S+ user manual section 8.2.

Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.

What you may notice

• Code 188 on the display
• Drinks stopping
• Water coming out cold or not at all
• A tripped breaker or a warm smell near the machine

Possible causes

Listed in WMF's documentation

• A heater element or its wiring that has failed
• A heater switch or safety cut-out that opens early
• A temperature sensor that misreads the water heat
• A power supply problem to the heater circuit

Other likely causes — what usually sits behind error code 188 on this control. A technician confirms which one it is before any part is replaced.

• Heater element coated with limescale in hard water, so it overheats and the safety trips
• Wiring connector near the heater darkened from heat
• Safety cut-out tripped after the machine ran with low water

Safe checks before calling for service

How a technician diagnoses error code 188

1. Confirm code 188 with the machine isolated from mains.
2. Inspect the heater wiring and connectors for heat damage.
3. Measure heater element resistance and insulation to ground.
4. Check the safety cut-out for continuity.
5. Test the temperature sensor against a reference.
6. Replace the failed part and observe a full heat-up.

How error code 188 differs from similar codes

Code 188 is a heater error, whereas 88 is a boiler over temperature and 89 is a boiler that heated too slowly.

Technical reference

Document

WMF 5000 S+ User Manual, 8.2 Error messages and malfunctions p.108-109

Edition

Series 1950 33 4186 6010, 08.2022 (copyright 2018-2022 WMF GmbH; dated 05.08.2022)

Models / control

WMF 5000 S+, WMF 1500 F (Internal Storage)

Section

8.2 Error messages and malfunctions, pp. 108-109 (error number table); errors 9678/9679/9619 grinder blocked listed on p. 110 (Errors without error message table)

Checked

October 2026

We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.