French Bread doesn't rise at sea level
I have a Panasonic SD-YD250 breadmaker, probably not the best in the world but perfectly adequate for my needs since I make mostly French bread and don't fool around with fancy grains. It worked fine at 9,000 feet in the Colorado Rockies but since moving to sea level in the Pacific Northwest it's been a failure; the dough doesn't rise and the bread comes out heavy as a brick. The recipe in Panasonic's recipe book is simple and I haven't changed it or any of the ingredients nor altered the 6-hour French bread setting:14.75 oz bread flour, 1.5 tsp salt, 1 tbs butter, 10.5 fl.oz water and 1 tsp dry yeast. Someone suggested using more flour or less water; another suggested 2 tsp dry yeast instead of one. Neither of these suggestions made any difference. I like Panasonic's recipe because it doesn't call for adding sugar or powdered milk and used to produce nice fluffy French bread in the mountains but it's just not the same down here on the coast. Is my machine broken? Is there too much humidity?
I know it sounds trite but have you checked the yeast to see if it's working? Most of the time we needn't bother with proofing our yeast but given your results at sea level, it can't hurt. The old fashioned way for active dry yeast is to take a bit of yeast and put it in some warm water that has sugar added to it. Good yeast will produce some bubbling in the water within 10-15 minutes indicating yeast activity. Instant dry yeast will do the same. No bubbles means you need to make a trip to Walmart or the local grocery store for some new yeast.
If you're using a municipal water source, too much chlorine in the water may be a problem. You could try bottled water or letting the water off gas overnight by covering the bowl of water with a cloth towel.
Modern dry yeast is reliable in almost all locations but if it has been exposed to high heat or excessive humidity during storage, it won't recover its properties. My personal experience is that bulk packaged yeast, will retain its properties for at least a few years if it's kept in an air tight container and stored in a freezer.
make a massive difference in timing for dough to rise. When you are at the higher elevation, then your air pressure is significantly less than at sea level, and so the boiling point of water is lower, final "cooked" temperatures are lower, and dough rises (ferments / proofs) faster.
Since your recipe worked perfectly at the higher elevation, then I would suspect that the timing in the machine is not right for sea level. You likely will need to experiment with either lowering the hydration of the recipe, increasing the yeast amount, or (most importantly) significantly increasing the time allowed for fermenting and proofing of the dough. This set of suggestions from King Arthur Flour are for modifying recipes to use at higher elevations, so might be helpful to you now if you just use the reverse: http://www.kingarthurflour.com/learn/high-altitude-baking.html
I'm not familiar with your machine, but your best bet may be to contact the manufacturer and find out what they suggest for you to continue with successful results. I hope you find a solution!
Thanks all for the info and I think yeast is my problem. The Fleischman's breadmaker dry yeast I bought was in a twist-cap bottle, unfrozen, so I thought I could keep it unfrozen in a kitchen cabinet. In reading the label -- duh, probably should have done it long ago -- it says to store it in the freezer, use within 6 months and never beyond the date on the cap. The hardly legible date on the cap was Dec. 2015. My face is red. All I can say in my defense is that the bottle contained far more yeast than I could ever use in six months. I never froze it but used a lot of it throughout 2016 in Colorado and it worked just fine, and only stopped working when I arrived in the Pacific Northwest in September 2016. That said I'll buy new yeast and stop kicking the breadmaker.
try using no salt!