Safety: Turn off the breaker before opening any electrical compartments.

Steps:

Check breaker: Locate the dedicated breaker for the heater and ensure it is ON. Reset if tripped; if it trips again immediately, stop and call an electrician or technician.
Inspect service switch: Some installations include a local disconnect switch near the heater. Verify it is in the ON position.
Open junction box: With power off, inspect the electrical junction box on the heater for loose wire nuts, burned insulation, or water intrusion. Tighten connections and dry any moisture.
Internal fuse: Many Lochinvar heaters have an internal low-voltage fuse on the control board. Check and replace with the exact same rating if blown. If it blows again, a short circuit exists and requires professional diagnosis.

If the display remains dead after these checks, the transformer or control board may be faulty.

Heater will not start at all; no display, no lights, completely dead.

Possible Causes