Remove the vent cover and see if you can reach and feel the hoses connected to the exchanger, to see if at least one red hose is fairly warm. If not, then it’s common for a zone pump to have a valve stuck shut.
I guess from what others have reported here you can gently rap on the back of a pump to jar the valve open. I’d shut off all thermostats except the one controlling the cold exchanger and leave that one set at say 80. Then see which pump, located behind the AquaHot’s cover at the bottom front, is “humming”. That’s the one with an apparently stuck valve, not letting hot fluid through the lines. Others here that have had to do this may elaborate, and I’ll have to defer the headlight issue as well.
Joel
In the photo, one pump is seen in the lower left with ”Papst” printed on it.