Understand Mitsubishi Electric P4 drain-sensing faults, distinguish them from P5 and prepare model-specific information for service.
Tell us what you need—we’ll call you back fast.
Updated 2026-09-18 · CANRO Heating & Cooling
Quick answer: On the Mitsubishi Electric equipment documented in the PEA-M LA2 manual, P4 identifies a drain-sensing fault; its detailed diagnostic section addresses a drain float-switch connection abnormality. Confirm the indoor model and applicable manual before using that explanation. P4 is not, on its own, proof that a drain is blocked or that the pump needs replacement.
Mitsubishi Electric and Mitsubishi Heavy Industries are separate manufacturers. Do not use a fault table from one to diagnose equipment made by the other simply because both display P4.
Record the complete indoor model, outdoor model and controller where available. A concealed ducted unit, cassette and wall-mounted head can use different drainage arrangements. The relevant indoor documentation matters when investigating the sensing circuit.
Use installation records or safely visible labels. Do not remove a ceiling panel, climb to an indoor unit or open an electrical cover to collect information for a booking. Ask the technician to obtain inaccessible identifiers during the assessment.
The cited manual lists P4 as a drain-sensor error and explains a float-switch connection fault in its detailed section. It describes P5 separately as drain-overflow protection. That distinction is important: a sensor or circuit concern should not automatically be diagnosed as the same problem as actual water backing up.
The broad code label still does not establish the failed part. A qualified technician needs to assess the relevant connection, circuit and equipment condition against the exact model's procedure. Do not bypass a float switch or copy a service-manual test into homeowner troubleshooting.
Note whether the message appears immediately, during cooling or after the unit has operated for a while. Mention recent installation, maintenance, ceiling work or other activity near the equipment. If water is visible, record its location from a safe position.
A dry floor does not prove that every drain or sensor condition is normal. Conversely, a water stain may have another source. Keep observations separate from the diagnosis and provide photographs showing both the affected area and its relation to the unit.
Do not pour water or cleaning chemicals into the unit, adjust its mounting, disconnect drainage, open the electrical compartment or repeatedly cycle the breaker. Keep clear of wet electrical equipment. The aim is to preserve useful information without turning a sensing fault into a hazardous test.
Ask which equipment manual was used, what abnormality was found and what work corrected it. If a sensor, connector or board is recommended, request the basis for that recommendation. If drainage work is also needed, have it identified separately in the scope.
After repair, ask which operating and drainage checks were appropriate and completed. If a condition could not be verified during the visit, record the follow-up arrangement. Clearing the display alone does not explain whether the underlying problem was resolved.
Does P4 mean low refrigerant? The manual referenced here concerns drain sensing and the float-switch circuit. It does not support diagnosing a refrigerant shortage from P4 alone.
Can I bypass the float switch to keep cooling? No. Do not defeat protective or sensing components. Leave circuit testing to the appropriately qualified technician using the equipment procedure.
Does P4 always mean a failed pump? No. The code does not establish that component diagnosis. Ask for the actual findings before approving parts replacement.
Is resetting the breaker a repair? A disappearing code is not proof of a repaired connection, sensor or drainage problem. Follow the owner's instructions and arrange assessment if the condition returns.
Tell CANRO about your equipment, your Greater Vancouver location and the question you need answered.
📞 (604) 359-1081 Contact CANROTechnical references checked 2026-09-18. The planning examples are illustrative; equipment instructions and project requirements must be checked for your home.
For help with a residential HVAC project in Greater Vancouver, contact CANRO with your equipment details and the question you need answered.
“Canro does an amazing job! Super professional and skilled with everything—boilers, furnaces, and AC. Always a pleasure working with them!”
“Five stars for Canro. We needed a replacement of a 30-year-old boiler. A new high-efficiency unit was installed—clean, professional work.”
“I can’t speak highly enough about George, who was recommended for a boiler service call for my parents’ home. George is excellent.”
25+ years keeping Metro Vancouver homes comfortable. Honest advice, upfront pricing, work that lasts.