Mitsubishi Electric fault code P8
Pipe temperature abnormal.
What P8 actually means
The pipe temperature is not where the unit expects it to be for what it is being asked to do. In practice that almost always means the refrigerant charge is low or something is restricting flow through the system.
What causes it
- A refrigerant leak, most often at a flare joint on the outdoor unit
- A blocked or dirty outdoor coil so the system cannot reject heat
- A failing outdoor fan
- A restriction in the line-set or expansion device
- A pipe thermistor that has drifted or failed
Most likely first. That order is from what we actually find on site, not from the manual.
Safe to check yourself
No tools, no covers off, nothing to do with gas, refrigerant or wiring.
- Look at the outdoor unit and clear anything growing against it or blocking airflow
- Check the indoor filters and clean them
- Give it 30 cm of clear air on every side
What we check on site
So you know what you’re paying for.
- Gauge the system and compare superheat and subcool against Mitsubishi's spec
- Electronic leak detection on the flares and the coil
- Check the outdoor fan and coil condition
- Test the pipe thermistor resistance against the table
Can you keep using it?
You can, but running a split system low on refrigerant is how you turn a flare repair into a compressor replacement. The compressor relies on refrigerant for cooling and lubrication. If it is throwing P8 regularly, turn it off and book it.
What the fix usually involves
If it is a leak, we find it, repair it, pressure test, evacuate and recharge to weight. Re-gassing without finding the leak is a bandaid and we do not do it, because you will be back in a year with the same fault and less compressor.
Is it worth fixing?
That depends almost entirely on how old the unit is. Past about ten years on hot water and gas heating, and twelve on aircon, a significant repair usually costs more per remaining year than a replacement does — and it’s the same point at which the VEU rebate is worth the most, because old inefficient appliances are exactly what the scheme pays to remove. If yours is young and the fault is a component, we’ll fix it and say so.
Repair or replace? The 10-year rule, and what the rebate is worth →