My son is 8 & has been sleepwalking for 4 years. He's irritable during the day.  what should we do? His pediatrician wasn't  concerned.

Sleep walking. Sleep walking is unfortunately a common problem. For children it falls into the category of sleep cycle problem. You might try waking your child after he falls asleep (maybe an hour or before you go to bed) and see if that shifts the cycle enough to eliminate the sleep walking. No side effects at least ad might everyone rest better.
Mostly benign. Most of the time, sleepwalking is benign and will go away with time. It is a very common childhood sleep disorder. That being said, you should ensure the safety of your son, so he doesn't get hurt. If he is irritable during the day, he may have a sleep disorder (like osa). I would see a sleep specialist.
Chronic sleepwalking. Given that you are concerned about your 8 yr old's sleepwalking and daytime irritability, I think it best that you have your child evaluated by a pediatric sleep specialist or a pediatric neuropsychologist. They are good resources to discuss strategies to refine your child's sleep routine and hopefully reduce irritability and provide reassurance.
Sleepwalking. Approximately 15% of children between 4-12 years of age will experience sleepwalking. Generally sleepwalking behaviors are resolved by late adolescence. (emedicinehealth. Com). For children and adults, sleepwalking is usually a sign of lack of sleep, intense emotional problems, stress, or fever. Unless the child is hurting himself or having psychiatric symptoms, no testing is necessary.