Hot Spring Vanguard not heating

[Tempus]

I have a Hot Spring Vanguard (late 2008 manufacture).  It stopped heating suddenly.  I don't recall it being just after a fill (it took me a while til I got around to dealing with it).  The pumps all seem to be working - all the jets work, bubbles from the hot water inlet so the circulation pump is working.  No blinking lights or error messages.  Shutting off the breakers did no good.  Testing the heater I got around 2.5 ohms.  My understanding is it should test at 8-15 ohms so I figured that must be it.  I replaced the heater and have exactly the same problem. Everything appears to be working, but no heat.  Any ideas? Thanks in advance!

[Tempus]

I should also mention that the ready light is not on, suggesting that it’s not a thermostat issue. Any ideas about what the issue might be would be appreciated. Thanks!

[castletonia]

Not a service tech here, but I'll try.  What temperature is the water and what does the display read?  My guess would be that it is not a control thermistor and the fact that everything else works would rule out a hi-limit thermistor.  If the circulation pump is working and it is a brand new heater, my guess would be the heater relay circuit board.  Is there voltage going to the heater?