Rinnai E- Series Troubleshooting Manual page 31

WARNING: Turn off power and water supply to the boiler before removing or installing any parts.
and
T1 T2 (swapped).
T2 temperature is measured to be higher than T1. Check
resistance value of T1 and T2 (See resistance chart under error
19 for resistance values. Replace T! and/or T2 if found to be
defective.
T1 Pressure Transducer
T2 sensor
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