You're assuming it's the head that's failed.
Did you have the whole valve changed last time? If it was just the head the body could be seized almost fully open which would not allow the microswitch to work and would give the symptoms you say you have
Did you have the whole valve changed last time? If it was just the head the body could be seized almost fully open which would not allow the microswitch to work and would give the symptoms you say you have