In brief

Fault code P6 on Mitsubishi Electric Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz- means: Fault code P6 indicates that the freeze or overheat protection of the plate heat exchanger has been activated. This code can relate to anti-freeze protection in cooling or heating mode, as well as anti-overheat protection in heating mode. Most common cause: The main cause is an anomaly detected by the temperature sensors (TH6, TH32, 63HS) or compressor frequency, suggesting reduced water flow, incorrect refrigerant charge, a blocked refrigerant circuit, or a malfunction of the water pump or outdoor fan. First action: Identify if the anomaly occurs in cooling mode (TH6 < -5°C or -2°C) or heating mode (TH32 < 15°C).. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).

According to the Mitsubishi Electric service manual, fault code P6 triggers in cooling mode if TH6 remains at -5°C or below for 10 seconds.

P6 • Mitsubishi Electric • Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-

Fault Code P6 Mitsubishi Electric: Causes, Diagnosis and Solution

Fault code P6 indicates that the freeze or overheat protection of the plate heat exchanger has been activated. This code can relate to anti-freeze protection in cooling or heating mode, as well as anti-overheat protection in heating mode.

Source: Mitsubishi Electric documentation (service manual – according to product reference) · Updated on 16 June 2026

← Codes erreur Mitsubishi Electric

Équipe Ask Marcel

Techniciens CVC certifiés

Rédaction et validation terrain par des installateurs PAC, clim et chauffage. Données croisées avec plus de 50 000 fiches pannes documentées.

What does fault code P6 on Mitsubishi Electric mean?

The main cause is an anomaly detected by the temperature sensors (TH6, TH32, 63HS) or compressor frequency, suggesting reduced water flow, incorrect refrigerant charge, a blocked refrigerant circuit, or a malfunction of the water pump or outdoor fan.

Symptômes

Display of fault code P6 on the control unit.
Stoppage or limitation of heating/cooling function.
Activation of freeze or overheat protection.
Temperature anomaly in the plate heat exchanger.

Diagnostic

1. Check Mode and Sensors

Identify if the anomaly occurs in cooling mode (TH6 < -5°C or -2°C) or heating mode (TH32 < 15°C).
Check specific temperature and compressor frequency conditions during detection (e.g., TH6 < -16°C for 10s during defrost).

2. Inspect Hydraulic and Refrigerant Circuit

Check water flow, clean filters, and inspect pipework for leaks or blockages.
Check refrigerant charge and circuit condition (blockages, linear expansion valve).

3. Check Electrical and Mechanical Components

Inspect the water pump and outdoor fan (motor and control).
For anti-overheat protection (TH3), check air ducts, filters, and fan motor resistance.

How to reset fault code P6 on Mitsubishi Electric?

First, check the hydraulic circuit by verifying water flow, cleaning filters, and looking for leaks. Next, check the refrigerant charge and the condition of the refrigerant circuit, including the linear expansion valve. If necessary, inspect the water pump, outdoor fan, and internal components of the indoor unit for overheating.

When should you call an F-Gas engineer?

This code appears during a critical thermal anomaly detected by thermistors TH6, TH32, or pressure sensor 63HS. It signals either a risk of heat exchanger freezing (prolonged low temperatures) or circuit overheating (high temperatures with low compressor frequency).

Affected models

Mitsubishi Electric Ecodan PUHZ SW50VKA BS
Mitsubishi Electric Ecodan ATW PUHZ W50VHA BS
Mitsubishi Electric Ecodan ATW PUZ WZ
Mitsubishi Electric Ecodan PUHZ HW140VHA2 BS
Mitsubishi Electric Ecodan PUHZ HW140YHA2 BS

Field context

Technical source data

Fault code P6 activates freeze or overheat protection of the plate heat exchanger. In cooling mode, it triggers if TH6 remains ≤ -5°C for 10s, or if TH6 ≤ -2°C with minimum compressor frequency for 5 min after 6 min of operation. In heating mode, it occurs if TH32 ≤ 15°C and TH6 remains ≤ -6°C (30s post-defrost) or ≤ -16°C (10s during defrost). An overheat variant (TH3) may also be involved. Causes include reduced water flow, incorrect refrigerant charge, blockages, or pump/fan failures. (Sources: Extract 1, 2, 6)

Sources: Ecodan ATW PUHZ W50VHA BS Service — ecodan-atw-puhz-w50vha-bs-service.pdf (p. 21) · Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-sw50vka-bs-service-manual-och525c.pdf (p. 28) · Ecodan ATW Databook (PUZ WZ) Vol.1 .0 — ecodan-atw-databook-puz-wz-vol-1-0.pdf (p. 128)

Questions fréquentes

What are the exact trigger criteria for fault code P6 in cooling mode?

Fault code P6 triggers in cooling mode if the heat exchanger pipe temperature (TH6) remains at -5°C or below for 10 seconds. Another condition is that TH6 remains at -2°C or below while the compressor runs at minimum frequency for 5 minutes, after the compressor has been running for 6 minutes.

How do I diagnose the cause of a fault code P6 in heating mode?

In heating mode, fault code P6 activates if the inlet water temperature (TH32) is 15°C or below, combined with one of these conditions: TH6 remains at -6°C or below for 30 seconds one minute after defrost starts, or TH6 remains at -16°C or below for 10 seconds during defrost. Causes include reduced water flow, incorrect refrigerant charge, or a faulty expansion valve.

What are the first troubleshooting steps for a fault code P6?

First check the hydraulic circuit: verify water flow, clean filters, and look for leaks. Then inspect the water pump and outdoor fan. If necessary, check the refrigerant charge and the condition of the refrigeration circuit, including the linear expansion valve, following component check procedures.

Besoin d'aide pour ce diagnostic ?

Marcel analyse vos codes erreur et vous guide pas à pas avec des réponses sourcées.