In this study we analyzed the dose response of natLiF:Mg,Cu,P (MCP-N) detectors in two different TLD readers (Harshaw 5500 and Toledo 654 Vinten) at 7 dose levels, ranging from 0.5 mGy to 5 Gy, for different heating rates (2 °C/s, 5 °C/s, 10 °C/s and 15 °C/s) and using 2 protocols: one without pre-heating and a maximum reading temperature of 255 °C and one including external pre-heating before the readout for 20 min at 100 °C and maximum temperature of 230 °C. The results show a upralinear behavior for Harshaw 5500 reader at high doses which is more pronounced for the fast heating rates. For the 15 °C/s heating rate, the supralinearity starts at 2 Gy for the protocol without preheating and at 0.5 Gy for the protocol with pre-heating reaching up to linearity indices of respectively 1.42 ± 0.05 and 1.67 ± 0.05 at 5 Gy. The 2 °C/s heating rate does not show supralinearity up till 5 Gy. The Toledo 654 Vinten reader shows no supralinear behavior. The shape of the glow curves is different between readers and reading protocols while the glow curve peaks shift towards higher temperatures for increasing heating rates due to thermal lag effects. This study demonstrates the different behaviors of TLD readers, for different heating rates and two types of protocols with an important concern for a Harshaw reader.