Don't feed old honey to the bees...
Old honey contains high levels of HMF(hydroxy-methyl-furfural) which for humans, is harmless, but for bees is a poisonous drug.
New honey contains 1 to 5 mg/kg HMF. In some parts of the world it is forbidden to sell honey for human consumption with more than 40 mg/kg HMF, even though it's harmless to us.
Honey deteriorates with aging and/or heating and with this the HMF increases. Only fructose will become HMF, so depending on the variatal of honey and it's fructose content, some deteriorate faster than others.
Heating the honey will raise it's HMF contents rapidly. The longer and/or hotter it is heated, the higher the HMF levels will become. Even when honey is stored at 68 degrees it's HMF content raises 1 mg/kg per month. Heating honey to 160 degrees will raise the HMF levels to more than 30 ppm in 5 to 10 hours depending on the fructose content.