A replacement thermostat must be wired by its labels, not the old wire positions.
If a replacement TH115 has no display, have the installer check that the incoming supply is connected to the replacement’s L1 (L) and L2 (N) wires, and the heating circuit to its LOAD wires. Do not copy wire positions or group wires only by color.
The attached replacement-base photograph shows the two middle wires as incoming supply and the outer pair as heating load. This is an example, not a universal layout for every TH115 generation.
Turn off power at the electrical panel before opening the box or correcting connections. A qualified electrician should verify the actual model, circuit voltage, connections and power-base/faceplate installation against its manual. If the unit still has no display after those checks, contact WarmlyYours technical support at (800) 875-5285 with the model and test results. A blank display alone does not establish which component has failed.
Sources: attached TH115 replacement photographs and TH115-AF-GA installation and wiring instructions.