my up-level heating system (gas heater) stopped working if the thermostat is at auto; fan can be on without warm air if switch the thermostat to ON from Aotu. Is this a thermostat problem or heat pump?
It may be a problem with the limit switch on the furnace or something like that. Most likely you'll need to get someone out to look at it.
In the mean time, make sure your thermostat is set to heat and auto. Unless you have one that doesn't let you specify heat/cool, generally On just forces the fan to run constantly, auto will make it turn on when it's heating or cooling but off the rest of the time.
You might also switch out the filters or clean them if you haven't lately.
Check that the gas valve to the furnace is turned on. It is pretty obvious but it happened to me in the fall... my 2-year just happened to get near the furnace for a couple of seconds and apparently the first thing he did was turn the (very tempting for a 2-year old) green valve and close the gas supply. We didn't realize what he had done until 3AM in the morning when we were all shivering.
Most likely this is not the problem since you say that having the thermostat on "Auto" will not even cause the fan to run (with the gas supply off, the furnace should start but then shut off after a couple seconds of it trying to light the burner)... but still, something to check anyway.
I had a problem like this, in my case it was bad setting of two thermostats (it was a bit unusual setup, as a gas heater connected as a backup source for the wood burning boiler, but it may still apply to you):
- external, controlling the temperature in the accumulation tank
- internal, controlling the working temperature of the heater (controlled by a turning knob on the heather, with one, two and three dots):
The problem was the temperature on the external one was set to ~65 °C, while the internal was set to two dots, which corresponds to ~50 °C. As a result, the external thermostat was saying "on" (which made the pump running, and allowed the heater to turn on), but the internal said "off" (the water is still hot enough), preventing the heating.
In a more common setup, you may have a room temperature thermostat saying "on" (room is cold), but the heater thermostat will say "off" (water in pipes is still warm enough). Unless the heater thermostat working temperature is set too low, it would still work fine, as the pump running will lead into water cooled down in radiators soon, and the heater should ignite eventually. Therefore my estimate is:
- you have set working temperature on the heater too low (one dot?)
- the heater is broken (ignition malfunction, or something like that)