In the morning, early, when my thermostat kicks back up, I hear a banging/rattle sound that I've determined is related to my humidifier. It only lasts about 10 seconds so by the time I get down to the basement it's gone. Turning on/off the humidifier doesn't recreate it either. When I turn off the humidifier completely it doesn't happen at all. I thought it may be the solenoid but still scratching my head. Currently I've been turning off the humidifier at night since it's super annoying to wake up to. Any ideas on how to troubleshoot/fix? The humidifier is the basic bypass type. The humidistat is also basic mechanical.

update Solved with a Sioux Chief 660-TC0 1/4' Icemaker Water Hammer Arrestor Tee from Amazon. Thanks to suggestion from user19919 below

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  • I hesitate to say it's fixed but one thing I did was to tighten the wire nuts, connecting the humidistat to furnace. I'm speculating that when the 2nd stage activated (in morning to get the temp up), the extra vibrations caused circuit to flicker and the solenoid hammered. Anyway it's been about a week 4 days and quiet. I do have high water pressure but the house has a pressure reducer. The water line is t'd off the hot water heater into a 1/4" copper line about 6 feet.
    – Andrew
    Dec 19, 2013 at 17:35
  • Nope, still happening, although not very often.
    – Andrew
    Jan 2, 2014 at 3:37

2 Answers 2


We got on Amazon and Plumber's Outpost carries Sioux 660-TCO Mini-Rester. It says it is for and ice maker. We have a 550 Aprilaire Humidifier and couldn't believe how easy it was to install! The smallest Home Depot carries is for 1/2 tubing. They gave me info on how to cut the copper pipe and hook the mini-rester to the humidifier. I had to buy a pipe cutter and small box of copper pipe, along with small brass washers for copper pipe (don't know what they are called). It cost me less than $50.00 for everything, and less that 30 minutes to attach it. I couldn't believe how easy it was! Not bad for a housewife!

  • I got the mini-rester last week and hooked it up over the weekend. It's been about a week and silence so far!! Thanks for the great suggestion
    – Andrew
    Mar 7, 2014 at 5:23

Water hammer is caused when flowing water abruptly stops and the change in velocity causes the piping to shake if it's not secured properly.

Look through the pipes you have access to and make sure they're securely fastened. If not, add some more clamps to secure them.

Contact the manufacturer of your humidifier. I'm not sure of the proper terminology but see if they have a replacement for the valve that controls filling the humidifier that closes slowly. My guess is in the morning the humidifier needs to refill itself, opens up the valve and when it's done it closes the valve quickly, causing the water hammer. Might also be another issue that they may know about.

They also make water hammer arrestors. These devices get installed in the copper lines and absorb the shock to reduce or eliminate water hammer. They will eventually need to be replaced (or if they are the round ones with a rubber bladder may need to be maintained) so install them somewhere accessible. Here's a video on installing a water hammer arrestor.

  • All that's needed to arrest water hammer is a vertical section of pipe, capped, near (preferably at) the device causing the problem. If it's fed from an elbow, pull it and put in a tee. Otherwise, tee in as close as you can get to the valve. The section of pipe captures an air bubble. Maintenance, when needed, consists of draining the pipes to refresh the air bubble(s) - the air bubbles act as shock absorbers or springs to cushion the water when the valve is suddenly shut and a mass of water is still rushing towards it. While "devices are sold", they are no better, and sometimes worse.
    – Ecnerwal
    Dec 16, 2013 at 0:50
  • Arrestors function the same way but make things a little easier and require less maintenance. Eventually the air bubble will dissolve into the water. The copper arrestors have a sliding piston that separates the air and water. The round one in the video looks like a Mini-Trol which is a lot like a mini expansion tank. Has a diaphragm between the air and water. Just like an expansion tank you can re-pressurize it with a tire pump. What makes them "sometimes worse"? Dec 16, 2013 at 1:57
  • You need direct access to "refill with a pump" - no access is needed for pipe stubs. Miniature expansion tanks fail the same way expansion tanks can and do - bladder failure and fill valve failure. In the long view, simpler can be better. If the plumber put in pipe stubs in 1950, all you need to do to make them work now is to drain the pipes once in a while. I'd not bet on that sort of service life from anything that choses complexity, valves, &/or moving parts. But pipe stubs don't have anyone selling them, while arrestors do...
    – Ecnerwal
    Dec 16, 2013 at 2:17

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