Dear A: You're getting good advice, but what's causing the problem? You have a restriction somewhere in the hot side of your plumbing. If a house is plumbed to code,(3/4in pipes)you should be able to take a shower without it being affected by other water use in the house, hot or cold. Anti-scalding is one of the areas addressed by code writers when they size plumbing. Another, is the future potential for pipes scaling up, (especially hot water pipes)which reduces flow. If you've had hot water re-circulating for several years, it's almost a certainty that your pipes are partially closed. Do you have a salt water softener? If you do, bybass it, your problem may go away. Treat your water with magnetic fluid conditioning, it should remove the scale within three months or so. I can help, but I can't advertise on here, so e-mail me & I'll send you some info. Good luck, Brian.