Edit to fix my original errors:
If I recall correctly, zone 2 (for back of coach) must have AH set to on - on the thermostat, then basement rotary switch set to temp you want heat to begin at? So rotary set at 40 degrees, basement will begin to heat at 40 and below?
Updated Correction: zone 2 is bath, zone 3 bedroom.
I believe the bathroom thermostat has to be on to activate the Bay Area thermostat.
Just tried different search terms and found the answer - which I will post in a minute or two on edit.
Edit:
Zone one is living room, dining room, dash. Thermostat turns on pump one and those blower fans.
Zone three is bedroom, thermostat tuns on pump three and blower fan.
Zone two is water bay in basement and bath. 3 ways for pump two to run:
1. Diesel AH burner active - pump two runs and radiator in bath and basement heat- but no blower fans run.
2. Bath thermostat set to temp to run, pump2 runs and heats radiators in basement and bath, only bath fan runs.
3. Basement thermostat set to temp to run, pump2 runs and heats radiator in basement and bath, only basement fan runs.
I have determined my basement thermostat (turn dial) is currently inop. Tommorow I will pull the cover and check the wiring.
Heat exchanger in wet bay question (http://www.foreforums.com/index.php?topic=27178.msg221722#msg221722)
The basement thermostat works TOTALLY separate from interior thermostats. When it calls for heat, the basement fan(s) come on along with pump 2. So, heating loop 2 fan coils get hot coolant through them (basement and bathroom) but only the basement fan comes on.
Hope this helps you all understand its operation.
Even if you set the basement thermostat to its lowest setting it does not appear to shut it off entirely. So if you winterize your coach and it gets cold the #2 pump will come on and the fans will blow across cold heat exchangers until the outside temperature warms up. It is this way on my coach, perhaps different on others.
I added an on/off switch that disables the thermostat so that no matter what the basement fans and the zone 2 pump does not come on while winterized and waiting.
Follow up: I put the temp sensor probe in ice water, and the basement AH heat exchanger heated and the fan came on. All was fine, just temp not low enough to set it off (we had some cold nights (though well above freezing) in Central FL and I was testing operation).