Low Flow Hot Water

[smquandt]

My hot water flow is now a very low volume, cold is fine, same results pump or city water. The hot low flow is at all faucets including the outside one. When I turn on the hot water I get 2-3 seconds of good flow then it goes to a trickle. There is a tempering valve flat on the floor under the Aqua Hot burner that I think may be the problem. I see a few previous posts on the problem of low hot water flow but no mention of this tempering valve.

Am I chasing a dead end here? Any suggestions appreciated.