Grundfos Magna 3 Knocking

Bob Gagnon plumbing and heating

I have a big boiler install I did a year or two ago and the customer contacted me today and said the large Grundfos ECM circulator was knocking, so she shut off the heat, and turned it back on a couple of hours later and the noise was gone, and everything was working properly. The boiler pressure is fine, any ideas?

Thanks, Bob Gagnon

hot_rod

Any check valves in the system?

Bob Gagnon plumbing and heating

Yes, this brass in line check valve is near the pump, the customer said the noise was coming from the box on the side of the circulator, I always pump away and use a spirovent air eliminator, air hasn't been a problem on any of my jobs since I started doing that.

Thanks, Bob Gagnon

ScottSecor

Was there a fault code on the Magna 3?

Bob Gagnon plumbing and heating

She didn't look before shutting it down.

Thanks, Bob Gagnon

hot_rod

Does the Magna vary it's flow somehow? Checks sometimes rattle just on low flow conditions.

Checks should size by gpm flow rate not pipe size, but the Cv is in full open position also.

Any flow less than rated has the check in a partial open position. Spring checks are best for hydronics, but can still chatter at very low flow conditions.

Mark Eatherton

Possibly could be harmonic back feed coming from flourescent lights? Grasping for straws here. I do know that harmonic feed back is a major issue with variable speed drives creating "noise" in the electrical circuits. Whooda thunk...

ME

ScottSecor

We've installed many Magna series circulators and have not had any noise issues. As a matter of fact they are often very quiet, especially when set to autoadapt. As far as knocking goes, if that boiler is a mod con I would think the noise could be from lack of flow. Are you sure the signal was going to the pump? Most of the time the Magna 3 has constant power and we turn them on and off with the built in relay (typically connected to the boiler or other outdoor reset).

Is there any chance the pump is not set to autoadapt (maybe speed III for example) and all of the zones/Danfoss valves closed since the outdoor temperature is finally warming up?

Bob Gagnon plumbing and heating

It was set for auto adapt, last time I was there. I'll have the owner check that, lm trying to diagnose it without taking a fifty mile trip into Boston.

Thanks, Bob Gagnon

Paul48

From a mechanical standpoint, it sounds like the check valve. The sound can transmit through the pipes. It sounds as though the flow was just at the point that the valve was shutting off. If it happens again have her vary the flow and if it goes away.....I see a 50 mile trip, in your immediate future.

ScottSecor

Ask the owner if the typically green circle at the top of the display was red, this would indicate an error.