03 on a Stiebel Eltron heat pump: High pressure switch: The high pressure switch has responded five times within a compressor runtime of two hours. The heat pump will shut down
Short answer
On a Stiebel Eltron heat pump, 03 means: High pressure switch: The high pressure switch has responded five times within a compressor runtime of two hours. The heat pump will shut down. 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: High pressure switch: The high pressure switch has responded five times within a compressor runtime of two hours. The heat pump will shut down.
Part involved: compressor / expansion valve / pressure switches.
When it shows: The high pressure switch has responded five times within a compressor runtime of two hours. The heat pump will shut down.
Likely causes:
- External filter on the return contaminated; pump seized; flow rate too low (all valves closed / heating curve too high).
On the LWZ 304 SOL / LWZ 404 SOL (integral ventilation units)
The manual says: High pressure switch: High pressure switch responded five times in five hours; heat pump shuts down.
Part involved: compressor / expansion valve / pressure switches.
When it shows: High pressure switch responded five times in five hours; heat pump shuts down.
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: unknown.
On the LWZ 304 SOL / LWZ 404 SOL (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: unknown.
Manual reset: unknown.
What you can check
On the LWZ 5/8 CS Premium, LWZ 5 S Plus, LWZ 5/8 S Trend, LWZ 5 S Smart (integral ventilation units)
- Note the fault number shown on the programming unit display.
- Check the appliance breakers/MCBs at the consumer unit are on.
- Check that some radiator/underfloor zone valves are open and the heating curve/room set temperature is not unusually high.
On the LWZ 304 SOL / LWZ 404 SOL (integral ventilation units)
- 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)
- Clean the filter; ensure pump function or replace; match heating curve; isolate the appliance across all poles from the mains for three minutes. If the fault recurs, inform your qualified contractor.
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.
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 16-17 · Reviewed 23 September 2026
- INSTALLATION LWZ 304 SOL / LWZ 404 SOL (English, via ManualsLib manual 1279865) ↗ · page 42 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026