I have two questions:

1. Customer drained water heater but never unplugged recirc pump. He hears it running but says it's not working. He has a holding tank in series with water heater. Did he ruin the pump, even though he hears it running? Says it's hot on one side of pump, other side is only warm.

2. He already bought a new pump on sale at box store. It appears to be the pump only from a Watts retro fit system, like the Grundfos comfort system. Can I install that pump as a replacement for the Laing he has in there now?

Thanks

The pump may be airlocked if the recirc line was not properly purged of air.

as far as i know, a pump is a pump is a pump. all they do is move water.
some faster, some slower.

The Comfort pump has male and female connections so it attaches to the hot water line and the hot water on the tank. The pipe connections would have to be modified to use it as an "in line" circulator.

I wouldn't scrap that circ, just yet. The water lubricates the bearings. Unless its extremely noisy, it may still be OK.Try bleeding the return line to the pump.

Yup, it was air locked. Got it