Like @ElectricSpidey said - - - scalding hot water - - - . If the heater heats water based on the water flow then double the flow rate (caused by doubling the pulse rate) isn't it possible you could get very hot water ? ? ? Hopefully the manufacturer set a temperature limit, one you can control; and likely you won't experience a flash of very hot water. But it IS possible. Again, you should talk to the manufacturer about this issue.

 

Be aware messing with the flow rate sensor could result in scalding hot water.

Not really in this sort of situation. It is not tampering with the temperature control, it is tricking the on/off (enabling) control. NOBODY has suggested changing anything in the temperature control portion. The problem with the system is that more flow is required to get the heater to switch on than the mandated low flow faucet can flow.
The X-OR/ or X-NOR circuit will indeed work but still more drive will be needed to activate the flow sensor input.

 

I have used many on demand (tank less) water heaters over the years, and none of them had a temperature control, just a power select…Low…Med…High, and the flow rate determines the temperature the water reaches. And a high limit.

The TS’s unit may be different. In fact all of the units I have used employed a pressure switch to determine minimum flow, not a counter.

So you could be right, but I wouldn’t make that assumption.

 

I would like to recommend one of CD/XR/LM-565 or CD-4046. The PLL circuitry for freq multiplication is shown at both datasheets. Only the case when its not be recommendable is when water flux is rapidly and frequently changing for orders of magnitude.

 

RE: Ebeowulf, thanks for interesting link, shall know it exists. I have experience, and much, about half-dollar price Hall sensor squirrel cages from e-bay, where aperture is untouchable. Thus, the frequency/flux ratio is genuinely sewed-in.

When the more accurate readings are needed, like calorific account, then exists a dozen of local and non-local products at price range 130-250 Eur, having software adjustable pulse rate.

 

Well, for what it's worth, the TS has been warned of possible negative outcomes, be they scalding, burning, bursting, explosions - etc. Hence forth, the TS has to take responsibility for the demise of the unit (or the household) in the event something goes wrong. If the TS is confident - so-be-it. I'm not. But then again, I'm not the one messing with boilers.

G'day mate.

 

I have used many on demand (tank less) water heaters over the years, and none of them had a temperature control, just a power select…Low…Med…High, and the flow rate determines the temperature the water reaches. And a high limit.

The TS’s unit may be different. In fact all of the units I have used employed a pressure switch to determine minimum flow, not a counter.

So you could be right, but I wouldn’t make that assumption.

I am responding to the TS request for help and since the TS has stated how that particular heater works, which is probably very new, and probably unique to California because of all their rules. AND please be aware that I am quite lacking in mind reading ability, especially at long distances, thus I am forced to go with what the TS says. And the statement about the flow measuring system seems quite reasonable.