I understand why hot water tanks can deliver water that's hotter for the first minute or so (heat rises to top of tank), but I have tankless hot water from an oil burner and for the first minute the water is very hot (160F) and then sometimes drops down to a much cooler temp (as low as 130-ish) but eventually settles down to about 145F and stays there. Is this sort of behavior normal from a tankless? If not what could cause this? We have a Watts Regulator mixing valve at the boiler that is set to the hottest setting--any chance the mix valve is too old and not working right?

Mike J.
Boston