We have a Water Furnace Synergy3D that is heating our floors. Ever since we turned the heat on this fall, the thing has been driving me nuts, as it would run for 10 minutes and then go off for 10 minutes. Then we received our electric bill and it was the highest I had ever had in my life. So, I called the guy who installed it and he never showed up. I finally got fed up and went out and looked the thing over. He installed a Johnson Controls A419 to sense when to kick on the heat pump. Unfortunately, he installed the sensor for it on the pipe between the heat pump and the water heater. Well duh, after about 10 minutes that pipe cools off and the heat pump kicks on again. So, I moved that to the hot output on my storage tank and put several layers of insualtion around it. This is working much better, but it seems like there should be some place to put it to more accurately measure the water temperature in the tank. It is not short cycling any more, but I do feel like the heat pump could run a little less. We are using a 100 gallon Marathon water heater for a storage tank. Any ideas on where that heat sensor should go so I can more accurately cycle the heat pump according to the temperature of the water in the tank??? Thanks, Kevin

That's probably as good a place as any. On a standard steel electric water heater tank you could tuck it between the steel and insulation behind the upper element cover, but that won't work as well on a Marathon.

OTOH I do believe Marathon might have provision for the high temp cutout to 'see' the tank temperature - this might take the form of a metal flap thermally connected to the tank water at or just above the upper element. You might try that location. A bit of aluminum foil folded around the sensor and laid flat against whatever surface you want the sensor to read may help with conduction. Ensure the whole arrangement is insulated and that aluminum foil is nowhere near any electrical connections

Highest electric bill of your life means little if it is less than you would have spent on other heating fuels.
That said, you do want your system to cycle less often for longer. Anywhere you can find a home for the temp sensor to do that, is fine by me.
Good luck,
joe

Look through your WF Manual to see how to check the Deadband in the Heat Control Module,HCM. Default on mine (FHP not WF) is one degree. Opening it up to 3 or 4 degrees made a world of difference for me.

My manual suggests wider settings for pool heater, etc applications vs house heat. I don't think this discussion takes into account buffer tanks in house heat installs.

ICM makes most of the HCMs so yours probably has similar capability for adjustment.

Dick

So what is the function of the sensor described in 1st and subsequent posts?

I'm sorry, by stat I meant the Johnson Controls A419 thermostat. Looking at the specs
it does have an adjustable dead band though. I would be nice to place that sensor in a
well inside that tank. 

One could probably obtain a thermowell that could be adapted to the element inlet on the water tank and then mount the thermostat sensor in the thermowell. That's ther industrial way to do this, but it probably comes with an industrial pricetag

I moved the temp sensor yesterday to the aluminum plate that is attached to the top element. I sandwiched it between the thermostat and the metal plate per "Engineers" suggestion and it is working great. Our heat pump did not kick on until about 7:00 last night after heating up the tank in the morning. Talk about a difference!!! The thing was running 4 or 5 times an hour. I don't get the logic my installer had of placing it on the pipe between the tank and the heat pump. This guy has been installing geo for 25 years. Apparently, not too many water based units!!! Thanks for everyone's replies. Kevin