I installed a Grundfos hot water recirc pump. This pump comes with flange fittings and rubber washers that seal the pump flange to a flange on the water line. The washer is about 2" in diameter and about 1/8 square in cross section. It fits in a circle on the pump flange. Two bolts on each side of the pump to mount it to the water line, compressing the washer between the flanges to make a seal.

I inserted the pump in the line, tightened the bolts and admired my work. There is a was small leak on the input side of the pump. About one drip per minute. So I made sure the bolts were compressing the evenly, and tightened them very tight. Still leaks.

I removed the pump, made sure the washer was not damaged and there was no debris on the flanges. I re inserted the pump in the return line and carefully tightened all bolts evenly, but not too tight. The output side is fine, the input side still leaks. I tightened those bolts. Still leaks, about a drop per minute.

The leak is definitely coming from the seal to the pump, not where I fitted the mating flange to the water line.

What else can I try?

Thanks in advance.

You have damaged that O-ring you need to replace it...buy a couple of spares

srloren

try adding a 3 hole gasket on the side that you think is leaking.
leave the round one in place.

They are usually "square cut" washers, not "o" rings, and also seldom the cause of the leak, if tightened properly.

Yes, it is a square cut washer. I have had no luck finding a replacement part.

Any suggestions on how to tighten? As tight as possible?

Just do not "bend" the flanges, unless you already have. you can get gaskets at many places. They are the same ones that B&G, Taco, and others use.



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Resolved. Thanks to all who replied

I never was able to find the square cut washers used on the flanges. I was able to find a kit containing the two flanges, 4 bolts and two washers. After trying everything I could think of I reexamined the leak. It was coming from the pipe fitting mating the pipe to the flange. I tightened it and the leak is gone!



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Grundfos flange gaskets are square cut and bigger than 1/8" for sure. I've never had a new one leak.

Where do you find these at? They all seem to have a 1 1/2" center hole.