Looks like this same thing happened to me. I posted this yesterday with no replies, but seems like I'm in the same boat:
Brewed the Houblonmonstre Tripel IPA extract kit from Northern Brewer three weeks ago. The only difference was that I used WLP510 Belgian Bastogne Ale Yeast instead of the kit's Wyeast 3522 Belgian Ardennes. Made a 1L starter 24 hours ahead of time, pitched right around 66F, and had the carboy in a room with a temp that varied between 60 and 70F. (I will admit that I definitely did not aerate enough.) I had a blow-off tube, and for the the first week, the sanitized water at the end of it was going like mad, and the carboy was sporting the best looking krausen I had ever seen. Measured OG was 1.082. I took a reading today (1st one) and was bummed to see it was only down to 1.036. And when I tasted it before taking the reading, I noticed that it was way too sweet.
The room temp where the carboy is probably got down to 60 around 5 times over the course of the three weeks. Think that was what stalled it?
I have some washed 3711 from a couple months ago. Should I whip up a starter and pitch it?
Thought I'd give an update on my stalled Belgian. After all the great advice I got from you guys, here's what I did:
Ended up rigging a beerquarium (as SWMBO calls it) with a rubbermaid bin, water, and an aquarium heater. Put the stalled carboy in there and let it heat up slowly for a day or two. Water temp around it was/is still holding steady in the mid-to-high 70s.
Made a starter of 3711 from a washed batch from a few months ago. Pitched about 24 hours later into the stalled beer. (I only used part of the washed yeast batch, and I don't have a stir plate, so I probably ended up underpitching, but still . . .)
After a week, gravity came down from 1.036 to 1.019.
Another week, gravity is down to 1.015. Just took the reading this morning.
Oh, and it is also delicious. It's gonna make a superb beer for the steamy Baltimore summers. And it's gonna be packing a punch at almost 9%. Will have to remember to switch to Kolsch (brewing next weekend) or the hefe (currently carbing) after downing one of these. But I digress.
My question is this: What to do now? This beer tastes pretty damn good as it is, and I was hoping to bottle next weekend. What if the 3711 is still going? Should I take it out of the beerquarium and "cold crash" in my 60-degree basement?
Any advice on next steps would be much appreciated. I am super pumped to have saved this beer (with all your help) and want to make sure I finish the job properly.
Cheers!