Heat pumps · Error codes · Kronoterm
TzKronoterm · TERMOTRONIC-controlled heat pumps (legacy WP / WPL / WPLV water-water, brine-water, air-water)
Tz on a Kronoterm TERMOTRONIC-controlled heat pumps: Alarm: overvoltage, undervoltage or inverted phase sequence in the electrical supply
Short answer
On a Kronoterm heat pump, Tz means: Alarm: overvoltage, undervoltage or inverted phase sequence in the electrical supply. 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: Alarm: overvoltage, undervoltage or inverted phase sequence in the electrical supply.
Part involved: phase/voltage monitor.
Likely causes:
- Phase failure.
- Wrong phase sequence.
Is it safe?
| 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.
Manual reset: After fixing the cause restart by holding ENTER for 3 s.
What you can check
- Note the exact message shown on the TERMOTRONIC display.
- Check the heat pump breakers in the consumer unit are on.
What the engineer will check
- Measure phases and voltage; correct phase sequence (authorised worker).
Who to ask for: heat pump engineer.
What you might notice
Sources
- KRONOTERM Owner's manual for heat pumps water-water, brine-water and air-water (TERMOTRONIC controller), Id 17-16-19-2972-05 ↗ · 17-16-19-2972-05 · page 51, 59 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026