The relay installed has a 9V rated coil with a nominal resistance of 225Ω. R18 should be 75Ω if the relay coil is to be driven with the rated voltage and current. It is currently 22Ω (pointing to poor circuit design), so the relay has been driven beyond its rated values. The coil current through 22Ω would be 48mA, so the resistor dissipation should have been 52mW in theory. That would be expected to make the resistor warm, but not hot. If it runs excessively hot, perhaps the coil has shorted turns from being over-driven.
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