Thank you everyone. I think @MikeRSmith nailed it with the "voltage sensitivity" on the original models. We'll probably replace this with a newer smaller model.
We have an Espar (Eberspacher) D 7L TD diesel heater on our 1984 CHB 47 which works perfectly well when turned on and keeps us warm all day. The only problem is that the ignition is unreliable. It seems to engage only after a long period of inactivity. If I turn it on today and turn it off...