Grundfos recirculating pump - where to mount sensor

rockjaw · Apr 16, 2016

Hi,
I just replaced a Grundfos hot water recirculating pump with one that has a temperature sensor attached to it - Comfort PM AUTO (UP 10-16 PM). The sensor is on a ribbon cable that can go up to 8 ft. I have a dedicated return line system.
Where should I place the sensor? I see two variants on the Internet - a) attached to the hot water outlet pipe at the top of the water heater, and b) attached immediately upstream from the recirculating pump.
Thanks.

johnjh2o · Apr 16, 2016

Upstream from the recirculating pump.

Mr_David · Apr 17, 2016

Depends on where your pump is and how close it is to the water heater.
The system has a dedicated return line.
Does it return to the cold supply line going into the water heater or to the bottom, attached to the drain cock port.

Logic tells me to put it where it will sense the water temp to turn pump on and off as needed.

putting it on the hot line coming from heater will shut the pump off as soon as the any water flow begins. The pump will be constantly cycling on and off, so don't put it there.

Upstream of pump is probably the best.
downstream closer to WH you may get false reading. while in standby, residual heat from WH can conduct heat back up the return line giving a false indication of a warm return line

frodo · Apr 17, 2016

,,,,,,,,,,,,,,,,,,,,,,,,,,

rockjaw · Apr 18, 2016

Thanks for all the replies! The return line comes to the pump, and downstream from the pump is attached to the drain cock port. I placed the sensor about 18-inch upstream from the pump. It seems to be working well. I figured that this placement will ensure that I'd get hot water at the distant faucets in the house more quickly than placement at the hot water line outgoing from the water heater.
18 inches because that's roughly all I have before the return line disappears behind a wall. The sensor is about 15 inches from the water heater - I don't think that radiant heat from the heater will be a problem.
Thanks again.