1. Last weekend we returned home to a cold house after being gone for the weekend.

Furnace switch in ON position
No tripped circuit
Pilot on

HVAC repairman comes next morning. Figures it is the transformer and replaces it. Voltage observed on one side but not the other side. Furnace works now.

2. 5 days later we wake up to a cold house:

Furnace switch ON
No tripped circuit
Pilot on

HVAC repairman comes. Flips on/off switch off, then on. Furnace comes on. He figures it is the damper so he sets it to always be open.

3. Next morning we wake up to a cold house:

Furnace switch ON
No tripped circuit
Pilot on
Damper now set to "open".

*I* flip on/off switch off, then on. Furnace comes on.

Question: what is going on? Sounds like some safety feature that is tripping. I don't want to get this know-nothing kid back out here, want to fix it myself or tell him EXACTLY what to do... I am not even convinced the transformer was broken the first time but replacing it did get the furnace to work. It could be that whatever the root cause of the problem is, it broke the transformer.

Any ideas are welcome.

Anyone?

Try cleaning the flame sensor.

Will do. Where is it??

You say that the pilot is on, does that mean that you have a free standing pilot or a pilot that lights each time the thermostat calls for heat.

Also you mention the furnace switch, which switch is this and where is it located.

Some of the new furnaces have a lock out built into the circuit board. And any time that it locks out it has to have to power turned off and then back on, is this what you are doing when you say you turn the furnace switch off and back on.

So tell us a little about the furnace itself. Like brand and model

Hi,
Thx--here you go--
Burnham series 2 model b gas
Standing pilot light
The switch is the one on the wall--the emergency call switch.

And yes what you describe sounds like the problem. Do you still think so?

Btw--it is a 2003 or 4.

What would cause the lock-out?