water heater t+p blow off

got a call about w. h. leaking. old one, but water released earlier from t. p. valve. will replace valve and install an expansion tank for thermal expansion. now here's my question. customer, a few years ago , had a plumber install a circ. pump. He used a close nipple and brass tee off the top
hot tap. the tp is threaded into the top of the t and the sensor can't be imersed into the tank much or at all. does it matter? this is the 1st discharge in 3 years. thank's tool