C.C.
When it comes to recirculating pumps, you need a plumber to install them who knows what s/he is doing. I would recommend that you speak with a commercial plumber (someone who works on large restaurants, specifically). Most larger restaurants use this technology, and if it's installed incorrectly, you will have problems (as you've discovered). You want to look for a plumber who specializes in new plumbing or remodel plumbing for large commercial projects - they will have the knowledge necessary to correctly install this. Residential plumbers, not so much.
My recommendation is that you call the plumbing service who installed the recirculating pump and ask to speak with the owner or service manager. Discuss your concerns, and tell them that this most recent fix did not resolve the issue. Tell them that you want a master plumber to come out and fix it, and that if he is unable to fix it, that you want your money back. You may or may not have any luck getting them to make it right for you, but it's worth a try. If you paid with credit card, you can always decline the charges, but I'd give them the chance to try and fix it first.
I have had a lot of luck with tankless hot water heaters. They aren't cheap, and if you're thinking about re-routing the hot water supply lines for this bathroom (which you will need to do, to some extent, to install a dedicated hot water heater for this bathroom), that may be a pretty pricey fix. Definitely get several quotes. Also, if the hot water heater will be mounted in an indoor space (utility closet, garage, etc), make sure the plumber is quoting on the proper type of vent pipe, per the manufacturer's specs. Some plumbers will try to cheap out on the vent pipe and using the wrong type can not only void the warranty, but damage the unit irreparably. Properly installed, you will love it though. Good luck.
