Unexplained Temporary T-stat outage

D107

At the family house for the porch Zone 2 we have a LuxPro PSD010B Low Voltage Thermostat wired to a TACO SR503 relay to a Buderus Logamatic 2107 to the Riello 40 F3 burner to G115/3 boiler. The porch being unused, the temp setting is kept all day to 60deg. Last week the alarm company's freeze alert went off in the middle of the night since the temp went down to 55. Never had this problem before and apparently it's been fine since. Last time I was there I saw the battery image flashing on the little screen and replaced them. The only things I can think of are:
1. Batteries were bad--but no battery image is flashing on screen.
2. Temporary power outage, but no other appliances were affected--no flashing clock lights on TV, oven etc.
3. Loose connection in the trail to Taco-Riello-Boiler.
4. Faulty Freeze alert module--but I believe someone did see the temperature reading of 55deg.
5. Faulty thermostat.

Any other ideas?

heathead

Check you 2107 for the temp setting of the outside (see if it matches the temp that it is currently outside). This is assuming that the 2107 is using the outdoor reset option. If the sensor goes bad it thinks its warm outside and won't fire boiler because its in warm weather shut down mode. Good Luck.

D107

Hmm, good thought. Though as far as we know the Main Zone 1 did not go off; that runs off a Room Sensor which is modified by the outside sensor. Only the Zone 2 off the T-Stat. One strange I've noticed about some electric outages up in my house: sometimes in the morning you could downstairs and find oven/tv clocks blinking but not upstairs. So if an outage is really brief can it really only affect parts of the house?

ratio

Part of the house losing power but not the rest could be caused by a loose connection - a real cause of electrical fires. Run your hand down the face of the circuit breakers in the panel. If you feel one too hot to touch, call an electrician & get him out there asap. Otherwise, get them out there to check it out.