On-demand tankless high volume capable water heating system

1. A method for determining the root cause of the lack of flow in an on-demand high volume capable fluid heating system for supplying a total heating power at a turndown ratio and a total flowrate of a fluid supply, said fluid heating system comprising: a controller; a plurality of heat exchangers fluidly connected in parallel, each of said plurality of heat exchangers comprising: a fluid conductor, wherein each of said plurality of heat exchangers contributes to said total heating power and a portion of the total flowrate of the fluid supply through said fluid conductor; an inlet conductor configured to connect the fluid supply to said plurality of heat exchangers at an upstream location of said plurality of heat exchangers; an outlet conductor configured for receiving the fluid supply downstream of said plurality of heat exchangers; an auxiliary conductor connecting said inlet conductor at a first location and said outlet conductor, said auxiliary conductor comprising a modulating valve; and a pump disposed downstream from said first location on said inlet conductor, wherein said pump is disposed upstream from said plurality of heat exchangers to prevent cavitation in said fluid heating system, said modulating valve and said pump cooperate to cause a recirculation flow through said auxiliary conductor and at least one of said plurality of heat exchangers in a first flow mode from said outlet conductor to said inlet conductor and said modulating valve controlling a bypass flow through said auxiliary conductor in a second flow mode from said inlet conductor to said outlet conductor and said controller operably connected to said modulating valve, said method comprising using said controller for:

(a) comparing a flowrate through each said heat exchanger as indicated by a flowrate sensor, with a flowrate through the other ones of said plurality of heat exchangers, wherein if said flowrate of each said heat exchanger is determined to fall outside of tolerance of said flowrates through a majority of the other ones of said plurality of heat exchangers, at least one of said flowrate sensor of said heat exchanger and a flow path of said heat exchanger is determined to be contributing to the root cause of the lack of flow in said on-demand high volume capable fluid heating system; and

(b) with a pump turn-on command received at said pump, comparing said flowrates of said plurality of heat exchangers to a threshold, wherein if a majority of said flowrates of said plurality of heat exchangers are disposed below said threshold, said pump is determined to be contributing to the root cause of the lack of flow in said on-demand high volume capable fluid heating system.

2. The method of claim 1 , wherein said tolerance is about 50%.

3. The method of claim 1 , wherein said threshold is about 10%.