High refrigerant pressure
The P1 error code on Mitsubishi boilers indicates high refrigerant pressure. Symptoms include 4 check room temperature display on remote.
Mitsubishi P1 means: high refrigerant pressure. The usual cause is condensatore sporco, ventola ferma. You can safely reset the boiler once — if P1 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does P1 Mean
The P1 code is shown by the boiler’s control board when it detects high refrigerant pressure. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| 4 Check room temperature display on remote |
Common Causes
Causes documented in the Mitsubishi service literature published by centriassistenza.org, cross-checked against the manufacturer’s fault-code table.
| Cause |
|---|
| Condensatore sporco, ventola ferma |
Safety Warning
P1 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
1. Identify which sensor is faulty from the error code (flow, return, DHW, flue gas, or outdoor). 2. Check the wiring — inspect the connections at both the sensor and the PCB for corrosion or loose terminals. 3. Measure the sensor resistance with a multimeter — compare with the manufacturer's resistance/temperature chart (typically 10kΩ at 25°C (77 °F) for NTC sensors). 4. If resistance is out of range (infinite = open circuit, near zero = short circuit), replace the sensor. 5. If resistance is correct, check the wiring continuity between the sensor and PCB. 6. If wiring is good, test the PCB input
How to Fix It
Have this checked: Condensatore sporco, ventola ferma
Refer to the Mitsubishi service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
TroubleAtlas Score
What Is the TroubleAtlas Score?
Every boiler model is independently evaluated and scored by TroubleAtlas across 6 dimensions: reliability, efficiency, parts availability, service network, value for money, and user satisfaction. The score helps you compare models and make informed decisions when choosing a new boiler.
See All Boiler Scores →Boiler Breakdown Cover
Boiler Breakdown Cover
Protect against unexpected repair costs. Cover plans include annual service, emergency callouts within 24 hours, and full parts replacement. Compare plans side by side and choose the level of protection that fits your home and budget.
Coverage Plans — Coming SoonConsidering a New Heating System
Considering a New Heating System?
If your boiler or heat pump is over 10 years old, replacing it with a modern condensing boiler or air-source heat pump could save you up to 30% on energy bills and significantly reduce your carbon footprint.
Compare Heating System Prices →
YouTube Channel
Watch the fixes. Follow the channel.
Step-by-step boiler repair guides, equipment reviews, and heating system comparisons from qualified engineers.
New fixes every weekFix in 5
Quick fixes for common boiler faults explained in under 5 minutes
Boiler Comparator
Side-by-side comparisons of popular boiler models
Boiler Reviews
Independent reviews with TroubleAtlas Score ratings
Find a Specialist
Don’t fix it alone. Find a trusted heating engineer near you.
TroubleAtlas connects you with vetted local heating professionals who can inspect, diagnose and repair your boiler safely — no guesswork, no unnecessary call-outs.
Local heating professionals are coming to your area
We’re onboarding Gas Safe registered and licensed HVAC engineers city by city. Check back soon, or search above to see current availability.
TroubleAtlas Pro
Get cited by AI. Get found by customers.
TroubleAtlas Pro puts your business in front of homeowners searching for exactly this fault, and structures your listing so AI assistants can cite you as a trusted source.
- ✓ Appear on error code pages viewed by thousands of homeowners
- ✓ AI assistants cite your listing as a verified local specialist
- ✓ Receive direct leads with customer name and contact details
- ✓ TroubleAtlas Certified badge for your marketing materials
Affected Models
Mitsubishi models that can display fault code P1:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Mitsubishi models | — | Possible |
Frequently Asked Questions
P1 is not classified as a high-severity fault, so the boiler can be reset once. If P1 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.