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Heat pumps
Heat pumps · Error codes · Viessmann
F.687Viessmann · One Base

F.687 on a Viessmann One Base: Communication error, EHCU

Short answer

On a Viessmann heat pump, F.687 means: Communication error, EHCU. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 1 source

What it means

The manual says: Communication error, EHCU.

Part involved: Communication error, EHCU.

When it shows: System characteristics:; The heat pump is switched off.; No function of connected components.

Likely causes:

  • Communication error in the EHCU electronics module.

Is it safe?

Does the heat pump stop?Yes
Engineer needed?Yes

The heat pump stops until the fault clears or is reset.

Resetting itself: Not stated per code in Viessmann document 6199893 GB 01/2026 (VSA00009).

Manual reset: User may acknowledge via HMI after noting the code (6249162 p.57); the message returns if the cause persists.

What you can check

  • On the HMI, tap the message and "?" to read the system characteristics and Viessmann's user tips; note the code (e.g. F.xxx) and text for your contractor (operating instructions 6249162 p.57).
  • Acknowledge the message once via the HMI; do not acknowledge fault messages several times in quick succession (6249162 p.58) - notify your contractor.
  • Check the heat pump breaker/isolator in the consumer unit is ON (do not repeatedly reset a breaker or RCD that keeps tripping).

What the engineer will check

  • Isolate the system from the power supply. Wait at least 2 min. Switch on the system.
  • Replace the EHCU electronics module.

Who to ask for: Viessmann-trained heat pump installer/service engineer.

What you might notice

Sources

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026