Which model water heater is it, and does it do anything when you turn on a hot water spigot. Like click, exhaust blower start then then turn off, etc?
Have you found the owners manual and tried the diagnostics? For my Girard I have called the Girard tech number several times with good results.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder