What model do you have? Some of the old Comnav products are no longer supported and you will be encouraged to buy a later model. Bummer, I know, they are expensive. I thought I would have to replace mine but managed to get it running again, because of their propensity to not support older models I would be very unlikely to buy another of their products, even though I really like mine and think it is well made. They are commonly used on large boats too.
Does yours get heading information off the compass? Check that the device on the bottom of the compass has not become loose. I dismantled my control head and cleaned all the contacts, about all you can do except for bad caps, that seemed to help as it hadn't failed since.
Your post doesn't say where you are or much else so that's all I can add.
"...Tongue tied and twisted, just an earthbound misfit..."