Loud rattling noise from themostatic mixing valve

UeqQminusW

I replaced my old Honeywell AM-1 thermostatic mixing valve which started acting up after 20 years. This is used to mix hot water from the tank with cold from the street for potable domestic use. I ordered a virtually identical new Honeywell AM-1, except that it now has built in spring check valves on the cold and hot inlets.

The problem is that the new valve makes a loud rattling noise whenever "hot" (mixed) water is drawn from the valve. It is fairly loud and annoying, relatively speaking. You can clearly hear it across the room.

Is this normal? What could be causing this?

Larry Weingarten

Hi @UeqQminusW , It seems this is a problem that should be taken up with Honeywell, but I'm wondering if the check valve in the hot side is something you can just pull out (and save!) and then see if the noise is gone? I'm guessing the check valves are there to prevent cross connection, but if you leave the one in the cold side, you should still have a properly operating system.

Yours, Larry

UeqQminusW

@Larry Weingarten I called Honeywell, and they did say it is not supposed to be noisy. They mentioned a couple of possibilities, the most likely of which is that something is simply loose inside. The other possibility is that it could be caused if the hot water pressure is not slightly higher than the cold water pressure. Nominally, they are about the same since the tank is pressurized by the cold water from the street... so I didn’t get the second explanation. Maybe they just meant that the hot shouldn’t be at lower pressure than cold. Like if you hooked the hot up via a pressure regulating valve for a hydronic loop accidentally.

Larry Weingarten

Hi, It seems we need to find out if it is the check valve/s making the noise. If you run a LOT of hot water, does the noise abate or stop? Running lots of hot would hold the check valve open and should quiet it. If it's still rattling under full flow, than it might be some other part and replacing the entire valve seems appropriate.

I'd expect hot water pressure to be slightly lower than cold under flow as there will be some pressure drop through the hot side piping.

Yours, Larry

Zman

I have heard the noise you are describing from that model valve several times. In those cases, the valve was in a mech room where it was not objectionable. I always figured it was a rattling check valve with minimal flow going past it.

infloorradiantheat

We had this problem. I just checked and it was a Honeywell AM-1. We removed it and took the check valve out. I see two identical check valves on my shelf so am not sure if they both came from the same mixing valve or if they are from different ones. We have three. It did solve the noise problem and since our mixing valves are behind heat exchangers it doesn't matter if water migrates through them in reverse when the system is off because the hot water is isolated to the boiler loop and not on these two loops.

UeqQminusW

Zman said:

I have heard the noise you are describing from that model valve several times. In those cases, the valve was in a mech room where it was not objectionable. I always figured it was a rattling check valve with minimal flow going past it.

I turned on four sinks and one shower. Combined flow is about 8 gpm. However, the noise is still there, although possibly reduced. Does that seem right? None of my other spring check valves are noisy. Maybe just a garbage product?

Larry Weingarten

Hi, It sounds like it's time to call Honeywell and get advice on how to fix or just replace the valve. I don't think it's an inferior product, but lemons happen

Yours, Larry