Dam thermometer off by 15 degrees!

so 2 weeks ago i tried making DFH 90 min IPA. my efficiency was horrible...less than 50%. 18lbs of grain should have got an og of 1.093. my SG was around 1.040 so i knew i was screwed but i could not figure out how i screwed up so bad.

well today i brewed up an IPA and when i was at my LHBS i decided to pick up a floating thermometer. when i heated up my water i compared the one i normally use with the floater. it is a dial one with a long steel rod so it attaches to the side if the pot and stick down into the water. well it was off by about 15 degrees, it read too hot. i checked it with 2 other ones i had laying around to confirm.

so now i know i mashed my DFH 90 at 134 instead of 149. i ended up dumping in some LDME and sugar but only got the OG up to 1.05 something....so i added hops for 60 minutes instead of 90.... so i made a screwed up 60 min ipa. put in the secondary today it tasted ok. very hoppy not much malty flavor

end of rant....

gutted mate, on the other hand it might end up been the best ale ever made

That sucks. Was the the culprit digital or analog? Have you used it before without problems?

So whats the plan of action? Sounds like time for a new gadget!

Thermapen! It has totally changed my brewing life. It was the best $100 I spent for brewing. Guaranteed accurate from the factory, quickest read time available, and it allowed me to document EXACTLY how far off my other thermometers are so they actually become useful tools!

I've had your problem as described here:
Thermometer Woes, FG problem.

Analog dial thermometers need to be recalibrated occassionaly. In ice water. Then turn the dial till the 32 degree mark lines up with the pointer.

it was analog. im gonna stick with the floater for now. nothing like an old fashion one with mercury. the previous batches were fine so i don't know if it was off then or not.

My floating thermometer is off by 6 degrees or so at mash temperature, but is fairly accurate under 80 degrees. I'd check the floating thermometer, too. In my experience, they aren't very accurate. I can't use mine for mashing.

guess i need to find something that is accurate. what is out there that doesn't cost 100 bucks?

There is tons of stuff out there for under 50 bux I have been looking at Lab Equipment websites. I think I am getting something like this. http://www.coleparmer.com/catalog/product_view.asp?sku=9020500

You do know you can calibrate the dial & Stem one that you have, right? I actually prefer boiling water. Heat water to boiling and keep at boiling. Insert thermo and allow to come to rest. Using pliers clam to hex on underside. Using hand rotate dial so that it reads 212. Not really difficult.

Could be worse. I had a thermometer that was reading 15 degrees high on a mash. So instead of mashing at 156 I was mashing at 171. I never got the FG below 1.021 on my hobgoblin clone.