J7-00 on a Daikin Altherma LT monobloc: Malfunction of intermediate heat exchanger thermistor
Short answer
On a Daikin heat pump, J7-00 means: Malfunction of intermediate heat exchanger thermistor. 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: Malfunction of intermediate heat exchanger thermistor.
Part involved: thermistor / pressure sensor.
When it shows: Intermediate heat exchanger thermistor detects an abnormal value (open or short circuit).
Likely causes:
- Faulty intermediate heat exchanger thermistor (R5T).; Faulty outdoor main PCB.
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: unknown.
Manual reset: Auto-reset when problem is solved.
What you can check
- Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) and note it, with the date/time, for your installer.
What the engineer will check
Who to ask for: Heat pump engineer (Daikin-trained).
Certification: Electrical competence to BS 7671 for sensor/PCB wiring; F-gas if a refrigerant-side sensor must be replaced.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- No heating on the Altherma LT monobloc: 1 report
Sources
- Service manual Daikin Altherma Monobloc CA EBLQ/EDLQ05-07CAV3 (ESIE15-08B) ↗ · ESIE15-08B · page 35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026