I have a water softener that performs on-demand regeneration based on the amount of water we use. Ever since we replaced our old water heater (gas-fired) with an indirect tank off a boiler, we have been regenerating every 2-3 days. Looking at the softener diagnostics, it thinks there is a constant 0.5 gallon/minute draw - this is not the case. Does anyone have any idea what could be causing this and how we can fix it? I've gone to scheduled regeneration, but I'd prefer the monitoring setup.

More details:

The softener is plumbed with a feed direct from the city, and the output tees to the water heater and to our cold water supply. The pipe from the softener to the heater is a combination of 3/4" PEX and 3/4" copper, totaling about 4 feet. The pipe is distinctly warm from the heater for about 18".

The heater is a large tank fed by a loop from our boiler, so it's not fired directly. We keep the tank at 160* and use a mixing valve to lower the output temperature. This is different from the old heater, which we kept at 115-120*.

The final weirdness is this. The water heater has two shutoff valves on the in and out sides. If I close the in-shutoff, the phantom water flow disappears from the softener diagnostics. If I close the out-shutoff, nothing happens.