I have oil fired furance tankless hot water.. I drainined the tank and all seemed to be OK.. Now I noticed that there is NO hot water at all... The house is the same. Cold water great and hot bad... If anyome can HELP.. THank you

Did you purge the air out of the system? It may have a manual reset limit switch on it that may have gone off due to air in heater.

No I didn't. And where would I fine the limite switch. Thanks.

If it has a manual reset limit switch then you would normaly find it near the top and it will have wires and a red reset button.