398 on a NIBE heat pump: Low pressure in climate system: External pressure monitor for the climate system indicates low pressure; check pressure and top up if necessary
Short answer
On a NIBE heat pump, 398 means: Low pressure in climate system: External pressure monitor for the climate system indicates low pressure; check pressure and top up if necessary. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
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What it means
The manual says: Low pressure in climate system: External pressure monitor for the climate system indicates low pressure; check pressure and top up if necessary.
Part involved: system pressure.
When it shows: External pressure monitor for the climate system indicates low pressure; check pressure and top up if necessary.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: no/unknown - No action.
Manual reset: Reset from the controller alarm menu ('reset alarm' / 'Reset alarm and try again'); alarm recurs if the cause remains.
What you can check
- Read the alarm text and the 'info/action' help on the controller display (VVM/SMO or S-series smartguide). NIBE's manuals let the homeowner select 'reset alarm' ('Reset alarm and try again' on S-series); if the lamp returns to normal the alarm has cleared. If it comes back, do not keep resetting: select 'aid mode' ('Auxiliary operation' on S-series) if offered, so any electric additional heat keeps heat/hot water going, and contact your installer. Read the heating system pressure gauge and tell your installer the value; only top up if your installer has shown you how to do it safely.
What the engineer will check
- Check climate system pressure, look for leaks, repressurise and check expansion vessel and pressure monitor.
Who to ask for: Heating engineer / heat pump installer.
Certification: None specific beyond competent heat pump installer; electrical work to BS 7671.
What you might notice
Sources
A code explains what the controller detected, not a confirmed root cause.