Hi, and first of all thanks in advance for the advice!

I have a relatively new (3 year old) home that just starting having low flow issues at all hot water outlets. It starts strong but immediately drops. I can turn a bath sink hot faucet on in the bathroom, then the tub, and the sink will reduce to almost nothing. This is consistent throughout the house. Cold flow is strong no matter how many faucets I turn on.

Can anyone suggest a good step-by-step set of diagnostics to isolate and correct the problem? I'm not exactly sure how to effectively narrow the problem down to the root cause, and if I bring in a plumber I would like to understand if they are following a sane diagnostic path or just guessing and trying stuff at my expense.

And I've heard that failing PRVs may cause this problem, but I don't understand how this type of a failure 'works'.

Also, if it matters, I have two hot water heaters in serial feeding the entire house. I regularly drain off the little bit of black crud that accumulates at the bottom of the tank.

Thanks!

To have a faucet that starts with high pressure and then dwindles to low volume [or pressure] is indicative of a partial blockage either by a valve that is not completely open or a valve that has failed. You do not have a pressure problem, you have a volume problem.

Well, I finally got a few free hours and started to tear apart the plumbing looking for the blockage. On a whim, I opened up several hot water faucets and tried opening and closing the valve on the feed to the hot water heater to see if I could hear any suspicious turbulence. Viola! There was a distinct high pitched rushing sound on the inlet to the first hot water tank, as opposed to the quite, low pitch whooshing at the other connections. Sure enough, I disconnected that inlet and there it was, a big chunk of plastic something jammed in the inlet! Must have made its way through the pipes and got hung up at the first major connect. Pulled it out, reconnected, and we're back to high volume, global warming volumes of hot water goodness!

Thanks!