We're having a strange problem. It seems that our main bathtub doesn't always put out hot water. When this is happening, I've tested other faucets including our other shower and the sink in the same bathroom as the bathtub I'm referring to, and they all have hot water. The problem is intermittent and although it happens throughout the day, it seems to happen more often during the evening hours (but again, all other faucets heat up quickly at this time). We do not have a hot water heater, as our hot water is heated by the furnace (oil, 4 years old). The pipe is insulated. This might sound strange, but sometimes redirecting the water to the shower rather than the tub faucet helps. Thanks for any help!! Mike

if the faucet employs a common cartridge(in other words single handle),then i would try removing the cartridge,then turn on the water to flush everything out,then check the cartridge itself for blockage.
depending on the type i would just replace it with new since you already have it apart.