boiler?

Wow!
The timer programmer is not calling for it to fire up
The room and cylinder stats are either satisfied or defective
The fan is not working
The pressure switch is not satisfied
The control board is defective
The pilot flame is not being ignited
The pilot flame heat sensor is defective
The main gas valve is defective
The boiler has tripped out due to overheat
The three port valve is defective

There may be other reasons

Take your pick...
January 2015