Getting same reading for Pre-boil SG as OG.

My friend and I have just completed our sixth all grain batch.  We had been getting a Brewhouse Efficiency of about 72%.  On our last two batches we started measuring our pre-boil SG which is around 71% in the boiler.  But, after the boil our OG has measured the same as the pre-boil SG (all hydrometer temperature adjustments were made) giving us a BE of around 55-60%.  Shouldn't our Brewhouse efficiency and OG reading be significantly higher after the boil?

Last batch:

Pre-boil SG= 1.056 @ 6.5 gallons
          OG= 1.056 @ 5 gallons

This batch:

Pre-boil SG= 1.042 @ 6.5 gallons
          OG= 1.042 @ 5 gallons

Yes, the SG should increase from the measured pre-boil (i.e., 1.055) to the final SG post-boil of say, 1.064.  The increase in gravity is a reflection of your evap or boil-off rate, so the hotter the boil, the more water vapor, leaving more sugars in less volume, higher gravity. 

Could a faulty hydrometer be the cause of the redudant reading?

Sure.  Water should be zero; use distilled water if possible. 

One oz of cane sugar to 8 oz of water should be 1.046.  (It equals 1# sugar to 1 gal water ratio.) 

Try to measure the sugar and water very carefully for that and test hydro at the standard temp for yours, usually either 60 or 68F. 

I tested the hydrometer in pure water it read 1.002 @ 77F or 1.004. I know this is off, but it still seems odd that I was getting the same reading for my pre-boil SG and my OG, and not two different readings that were both slightly off.

How and where did you measure the temperature.  I use to measure the temp in the class measurement tube but it was always cooling way to fast.  Now I just plop the hydrometer in the boil kettle before boiling, measure gravity and temp and then plop the #'s into BS.

My last measurements:

    preboil Gravity: 1.034 @ 150 F.
corrected Gravity: 1.053

cheers

I measured the temp and SG from a thief.  I didn't think of putting the hydometer directly into the kettle. I will probably try a digital thermometer and possibly a new hydrometer though. My readings still seem very odd.

Preboil - 1.022 @ 151F.
Adjust  - 1.042

OG  - 1.040 @ 78F
Adjust  - 1.042

Odd indeed!

The last test I'd do is check the hydrometer throughout the temperature range (in plain water) or at least at the temperatures in question and then do adjustments.

When you get a new one you can then compare the two.  Funny thing is, they'll probably be within a point.

cheers

Friends have had hydros "break, fail" on them.  I'm not sure what exactly happens in that case, but it does happen. 

I noticed that the cheap LHBS variety of hydro has a slip of paper inside the tube that moves.  If the paper moves, it can't hold tolerance very well.  That would explain the 1.002 reading of water. 

And although you can correct for temps out of range, I would think you'd get much better readings if you cooled the sample down to below 75F at least.  That's a pain, cooling 4 oz down quickly enough to get a reading, which is one great use for a refractometer.  The sample size is mere drops, which cool very quickly. 

Search for this string on ebay if interested:  Usually $38 delivered. 
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