Return NTC probe temperature reading °C / °F
The P03 error code on Immergas boilers indicates return ntc probe temperature reading °c / °f.
Immergas P03 means: return ntc probe temperature reading °c / °f. On this component the documented failure modes are the return sensor has failed — short circuit or open circuit. You can safely reset the boiler once — if P03 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does P03 Mean
The P03 code is shown by the boiler’s control board when it detects return ntc probe temperature reading °c / °f. 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 |
|---|
| The display shows P03 and the boiler stops until the fault is cleared |
Common Causes
The manufacturer does not publish a cause list for this specific code. The causes below are the failure modes documented for the same component on other boilers, confirmed by the service literature of 4 different manufacturers.
| Cause |
|---|
| The return sensor has failed — short circuit or open circuit |
Safety Warning
P03 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
Note the exact error code and check the manufacturer's installation and service manual for specific guidance
Check all visible wiring connections for security and condition
Power cycle the boiler — switch off at the mains for 30 seconds, then switch back on
If the fault recurs, check the fault history for related or recurring codes
Inspect the boiler for any obvious signs of damage, leaks, or unusual sounds
How to Fix It
Replace the fan motor assembly if bearings are worn or motor is not running
replace the air pressure switch if it is stuck or reading incorrectly
clear any flue or condensate blockage
repair or replace damaged wiring
if PCB is not providing the signal, replace the PCB
Measure the resistance of the return sensor with a multimeter and compare it against the manufacturer’s resistance-versus-temperature table; replace it if it is open circuit, short circuit or out of range.
Refer to the Immergas service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Immergas models that can display fault code P03:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Immergas models | — | Possible |
Frequently Asked Questions
Replace the fan motor assembly if bearings are worn or motor is not running. According to the technical documentation, this is the first check on the list for P03.
P03 is not classified as a high-severity fault, so the boiler can be reset once. If P03 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.