We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Sam Farrell"
saying something like:

My son in law has a central heating system that doesn't appear to have a
thermostat. There is no thingy on the wall that you can adjust.

It uses a ACL Drayton LP522 control unit. Does this have a built in
thermostat or do I need to fit one externally?

Many cheapskate *******s fitted CH systems with no stats, relying on the
boiler stat to do the work. Horribly wasteful, imo. Easy to update,
though.