17 on a Stiebel Eltron heat pump: Defrost time exceeded: The evaporator is not defrosted within the defined period; after ten successive occurrences the heat pump is blocked
Short answer
On a Stiebel Eltron heat pump, 17 means: Defrost time exceeded: The evaporator is not defrosted within the defined period; after ten successive occurrences the heat pump is blocked. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the LWZ 5/8 CS Premium, LWZ 5 S Plus, LWZ 5/8 S Trend, LWZ 5 S Smart (integral ventilation units)
The manual says: Defrost time exceeded: The evaporator is not defrosted within the defined period; after ten successive occurrences the heat pump is blocked.
Part involved: water flow / pump / booster heater.
When it shows: The evaporator is not defrosted within the defined period; after ten successive occurrences the heat pump is blocked.
Likely causes:
- Defrost not completed within time limit.
On the LWZ 304 SOL / LWZ 404 SOL (integral ventilation units)
The manual says: Defrost time exceeded: Evaporator not defrosted in defined time; compressor blocked after ten successive occurrences.
Part involved: compressor / expansion valve / pressure switches.
When it shows: Evaporator not defrosted in defined time; compressor blocked after ten successive occurrences.
Is it safe?
On the LWZ 5/8 CS Premium, LWZ 5 S Plus, LWZ 5/8 S Trend, LWZ 5 S Smart (integral ventilation units)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: electronics reset button / STB reset per manual.
On the LWZ 304 SOL / LWZ 404 SOL (integral ventilation units)
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: unknown.
What you can check
- Note the fault number shown on the programming unit display.
- Check the appliance breakers/MCBs at the consumer unit are on.
What the engineer will check
On the LWZ 5/8 CS Premium, LWZ 5 S Plus, LWZ 5/8 S Trend, LWZ 5 S Smart (integral ventilation units)
- Press the electronics reset button. If the fault recurs, inform your qualified contractor.
Who to ask for: Heating / heat pump engineer.
On the LWZ 304 SOL / LWZ 404 SOL (integral ventilation units)
- Follow remedy in LWZ 304/404 SOL installation manual section 9.4; causes largely parallel LWZ 5-8 list.
Who to ask for: F-gas/refrigeration-qualified heat pump engineer (R290/A3 flammable-refrigerant competence for R290 models).
Certification: F-gas certification for fluorinated refrigerants (R410A/R454C); flammable refrigerant (R290) handling training for R290 models.
What you might notice
Sources
- COMMISSIONING AND NOTIFICATION LIST LWZ 8 CS Premium / LWZ 5 CS Premium / LWZ 5 S Plus / LWZ 8 CS Trend / LWZ 8 S Trend / LWZ 5 S Trend / LWZ 5 S Smart (doc-00081766) ↗ · A 338916-45679-9862 · page 18 · Reviewed 23 September 2026
- INSTALLATION LWZ 304 SOL / LWZ 404 SOL (English, via ManualsLib manual 1279865) ↗ · page 43 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026