Re: 164 TS heater problems
1) The Thermostat. all Alfa thermos are poor and have a short life span, so it is definitely a candidate
2) The heater works by having permanent hot water passing through the heater matrix. It is introduced to the cabin by a flap which blanks off the air flow through the matrix when you want cold, and gradually allows more airflow through the matrix as you open the heater control. If the flap is stuck..no heat, but i'd look at the stat first.
If the temp gauge on the dashboard is not rising its 99% the thermostat, and I'd do that first. Yes it will stay cold for 200 miles..mine used to in cold weather until I sorted it out with a stat.