# Need Check Valve Help



## ckoch407 (Sep 30, 2009)

I have a client in a huge home that has an AO Smith Cyclone on one side of the house and a regular 50 gal AO Smith on the other. The home is 5-6 years old and has I think 12 bathrooms, 2 kitchens, and several butler/bar sinks. Both of the water heaters have a Grundfos recirc pump controlled with an aquastat so there are check valves on the cold inlet to the heater as well as the return lines. They complained about a noise coming from the water heater area at random and when I did my diagnostics this is what I found: When ANY hot faucet/valve is turned on the check valves make a clank. When turned off they make several louder clanks depending on how fast its turned off kinda like air/water hammer. When washing machine comes on they chatter also like air hammer, and they sometimes chatter at random when nothing apparent is on. Even in the middle of the night. The check valves are horizontal swing checks and they make the noise at both heaters simultaneously when it occurs, but more prominent at the big cyclone. I was thinking about replacing them with spring checks and installing a few AHAs on the water heaters. Any thoughts.


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## ILPlumber (Jun 17, 2008)

Soft seated checks should be used.

Sounds like hot main might also be undersized. Water is trying to rush back the return.

Change the checks and report back.


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## eddiecalder (Jul 15, 2008)

Is this only happening with the hot water (could be a PRV issue)? 
What type (if any) of expansion tank is being used?


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## ckoch407 (Sep 30, 2009)

Matt said:


> Soft seated checks should be used.
> 
> Sounds like hot main might also be undersized. Water is trying to rush back the return.
> 
> Change the checks and report back.


Thats kinda what I thought too about the back pressure, but was baffled that it just started after 5-6 years. I will report back soon as the jobs done. Thanks Matt.


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## ckoch407 (Sep 30, 2009)

eddiecalder said:


> Is this only happening with the hot water (could be a PRV issue)?
> What type (if any) of expansion tank is being used?


There is no expansion tank. There are calibrated PRVs on the hot ouutlet on both heaters. Yes only with the hot water.


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## eddiecalder (Jul 15, 2008)

What size is the hot main? 
Is there a recirc line?


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## ckoch407 (Sep 30, 2009)

eddiecalder said:


> What size is the hot main?
> Is there a recirc line?


Hot main is 1"as is the cold. There is a 1/2" return.


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## eddiecalder (Jul 15, 2008)

How fast does the clanking happen after opening a hot water valve?

I have installed a couple AO Smith Cyclones and have had nothing but problems with them. We installed 4 in a commercial building and upon start up two had broken hot surface ingnitors and another had a wiring problem with the display screen. 

When we finally had all for up and running we started to notice a "clanking". It turned out to be a debris clog ( looked like black metal flakes ) in the tapped tee that condensate plastic pipe connects to on the air intake line 90.

The AO Smith Tech told use to upsize the gas piping to 1-1/4" from the outlet of the pound to inches reg and reduce back down to 3/4 " (if i remember correctly) at the inlet of the appliance reg.

He explained that the upsize in the piping would help reduce a percussion effect on between the diaphragms of the regs ( causing flashing ). He also said to install the reg 36" away from the appliance ( for the same reason ).

None of this information is found in the installation instructions. 

This is probably not what is happening in your case but when it happened to me I thought it was water hammer at first.


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## Protech (Sep 22, 2008)

Your right on Matt. I had this exact same call 3-4 months ago and that was the cause. Go with a soft seated check valve and that will emininate the "clanking".



Matt said:


> Soft seated checks should be used.
> 
> Sounds like hot main might also be undersized. Water is trying to rush back the return.
> 
> Change the checks and report back.


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