I don't understand everything being asked, so add a comment any time.
Problem1 is excessive electric bill.
Suspect is new 120Volt Taco recirculation pump.
Look at motor nameplate for amps and watts and HP. Taco pump is usually robust 1/3 HP which is 252 watts or same as running four 60 watt light bulbs.
If pump runs 18 hours per day x 252 watts = 4536 watts or 4.5 Kilowatts per day
Buy a kill-o-watt meter that plugs into outlet, and plug Taco pump into the meter for 48 hours.
This will give you total watts used for that time period.
1000 watts = 1 kilowatt.
Electric bill is probably 12 to 20 cents per kilowatt.
So if Taco uses 4.5 kilowatts per day, that is $.54 to $.90 per day multiplied by 30 days.
So cost is $15 to $30 per month.
Problem2 is Taco runs too long.
Taco operates either by thermostat or by timer. You choose which mode by using slide switch that is usually located under the timer dial. Set switch to TIMER to use timer, and ON to use thermostat, and off to turn TACO off.
If Taco is set for thermostatic operation, the Taco might be defective. Or there could be crossover problem at single handled faucet.
Another problem could be air in the water line: install air vent.http://waterheatertimer.org/Crossover.htmlhttp://waterheatertimer.org/Water-heater-recirculation-system.htmlhttp://waterheatertimer.org/How-to-set-timers.html