Mark,

On Feb 1, 11:37 am, ransley wrote:
I thought all valves vary water output.

As Smarty says, my valve only adjusts temperature, and keeps the
pressure constant.

If its NG your tankless gas
supply is probably to low due to to small a supply pipe, have it
tested, its a common installer error.

It's an indirect coil in a oil-fired boiler.

Thanks for your suggestions,

David