Mysterious hot water comes and goes

First, thanks for an awesome website full of loads of information. I’ve learned a lot from reading these forums.

Now for my dilemma…

I have a 2.5 bath colonial, all copper pipes and a 1mth old 50gal hot water heater that’s been working perfectly since installed.

I’m currently renovating my master bathroom as the shower had a leaky drainpipe (actually a cracked copper pipe from rotted, sunken beams pressing on it…that’s another story). This bathroom has been out of commission for well over a year.

A plumber came to do some repairs and install a new diverter for the master bath shower. We shut off the house water, he installed it, then we turned it back on again. Well, ever since that day, the hot water is acting funny. I’ll turn on the hot water at a faucet and it’s burning hot, but then it slowly turns to luke warm and stays that way. If I then switch the water to cold and back to hot again, it returns to burning hot…then slowly turns to warm.

This happens at my kitchen sink, sinks in the other upstairs bathroom, the bath tub/shower…doesn’t matter where I am. I’m still not using the renovating bathroom.

Something interesting – If I turn on the hot water at the dual sinks in tub bathroom and wait for it to turn to luke warm…then, while they’re still running, turn on the bathtub to hot, it’ll cause the hot water to return to those sinks…but that tub won’t be hot.

It’s very strange.

I read somewhere that crud could be floating around in the hot water lines. As it makes it’s way to each faucet when turned on, it clogs the valve at each sink, causing less hot water to make it’s way out the line…not allowing the hot and cold to properly mix and pass through.

Do you think this is the case? I’d appreciate any advice you may have. Many, many thanks in advance!