You probably got some air into those zones when the ex-tank failed that is causing a flow blockage. A good purge, most likely assured by a good repair company, would probably get it back to heating again.
Radiant floors do not heat up quickly, so the quick shut down of the burner points to the boiler temperature rtising to the high limit setting and shutting down the burner because the water is not flowing to take the heat out of the boiler to the radiant panel.
Most control sets do not work on only the return water temperature.
» This message has been edited by Harold Kestenholz on 05 October 2003