1989 Soverign not heating. Everthing seems to be working. Cir. pump is working but not hot. Cir. Pump, heater, thermostat replaced last year. Any ideas?

Need to make sure the heater is getting the required voltage, wether it be 120 or 240 setup.
What style heater is it, that you replaced the old one with? Is it the pdr titanium? Make sure to check the reset on the heater if it has one, it may just need to be pushed in.
Just some ideas.

Not sure of the type of heater. I replaced the original one with an upgrade kit.