We present the first observations of microflare heating within an Active Region (AR) with SDO/AIA, Hinode/XRT and NuSTAR. NOAA AR 12333 (peaking at an estimated GOES class of ~A0.1) was observed over three hours on 29-Apr-2015 in both the EUV with SDO/AIA, and Soft X-Rays (SXRs) with Hinode/XRT. The Hinode observations were obtained during a co-ordinated campaign with the NuSTAR hard X-ray (HXR) focusing optics telescope (Harrison et al. 2013); NuSTAR is a highly sensitive focussing optics telescope sensitive to HXRs above 2.5keV, providing imaging spectroscopy. NuSTAR performed full-disk observations in mosaic mode, observing AR 12333 four times. We investigate the heating in the AR through the recovery of the Differential Emission Measure (DEM) from three separate methods: Weber et al., 2004; Hannah & Kontar, 2012; and Cheung et al., 2015. The DEMs from SDO/AIA and Hinode/XRT show multi-thermal emission, with the temperatures of peak emission measure (about 3-5MK) comparable with the isothermal spectral fits to the NuSTAR data. The DEMs also show a higher temperature component (above about 8MK), which has large uncertainties. This is not seen with NuSTAR, which may be due to short effective exposure times, resulting in a limited spectral dynamic range. We can however constraint this higher energy component by combining all three data sets and conclude that this emission should be weak and sharply falling off above ~6MK. We also constrain the non-thermal emission, comparing it to the thermal energy, to better understand whether or not the accelerated electrons are powering the heating in the microflare.