no pilot light stopped working no hot water and heating?

all ok yesterday today as the boiler calls for heat there is no pilot light ,i can hear from bottom right behind the time clock area a gentle continual electrical continual buzzz light a stuck scaleletrics motor and a faint tick tick tick sound as the flue fan ramps up and down. is it the gas solenoid valve stuck? if so how do i change it out and if it isnt what is it and how do i change it fix it regards r skedgell