Apparently no power at the transformer - is there a fuse somewhere. Model UCG 100-ER

No power going into the transformer means you have a bad fuse or kicked breaker,, if there power going in but none comeing out (24 volts) meaning a bad transformer,, if it's a gas furnace make sure the puch-in door switch is pushed in when checking it out

no power going into the transformer means you have a bad fuse or kicked breaker,,,,if there power going in but none coming out (24 volts) meaning a bad transformer,,,,,if its a gas furnace make sure the puch-in door switch is pushed in when checking it out

Is there likely to be a fuse interior to the furnacne - that is other than the CB at thepanel?

This began with a thermostat replacement where the old stat was removed without noting the wirign so I am guessing and am confused by the blue wire but connecting it to blue connection - could I have blown the transformer? We have power into the transformer (120V) and none out on G to R check, so I will change transformer but worried about blowing it again if the stat isn't correct.

Some, if not most, furnaces will have a 3 or 5 amp auto-style fuse on the board. Give that a looking. If you have 120VAC supply at the furnace then your breaker is not tripped. Double check your stat wiring first then replace the x-former.

Kick the breaker off anytime you are working on ,replacing tstat or transformer,, is the safe way
But yes its time to replace transformer for certain

Some, if not most, furnaces will have a 3 or 5 amp auto-style fuse on the board. Give that a looking. If you have 120VAC supply at the furnace then your breaker is not tripped. Double check your stat wiring first then replace the x-former.

Replaced Transformer and now have power to relay but no heat. Fan will now run if stat on manual fan and relay looks and ohms okay but furnace does not attempt to light. Pilot okay but had to relight