DHW Mixing Valve

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Phil May
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Post Thu. Mar. 27, 2014 4:51 pm

Quick question. Do you need a check valve on the cold side of a mixing valve to stop convection in dhw use.

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Carbon12
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Post Thu. Mar. 27, 2014 5:30 pm

I used a check valve on the cold water supply line to the boiler fill, cold water DHW supply and mixing valve, inclusive.

Edit: Oops, sounds confusing. I have one check valve.
Last edited by Carbon12 on Fri. Mar. 28, 2014 9:53 am, edited 3 times in total.
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lsayre
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Post Thu. Mar. 27, 2014 6:21 pm

I don't have a check valve on the cold water side of my mixing valve. Working fine for 3 years now.

I do have a check valve on my boiler water feed line.
-Larry

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Sting
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Post Thu. Mar. 27, 2014 8:30 pm

Phil May wrote:Quick question. Do you need a check valve on the cold side of a mixing valve to stop convection in dhw use.
no

the valve creates its own issolation
When you turn your boiler on -Does it return the favor?
I have finally lost my mind. Don't bother to return it. It wasn't working properly anyway!

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McGiever
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Post Thu. Mar. 27, 2014 8:31 pm

Some would use a heat trap pipe configuration instead of a check valve, but it would go on the hot side. :)
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mozz
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Post Thu. Mar. 27, 2014 9:23 pm

I have a gate valve between the input and output of the hot water coil. Adjusted accordingly. Am I doing it wrong?
Gouldsboro PA.


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Sting
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Post Fri. Mar. 28, 2014 6:56 am

You should have used a GATE valve. but other than that....

Are you doing it wrong - in this case it doesn't depend

The answer is YES
When you turn your boiler on -Does it return the favor?
I have finally lost my mind. Don't bother to return it. It wasn't working properly anyway!

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mikeandgerry
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Post Fri. Mar. 28, 2014 9:18 pm

The new ones from Honeywell come with a nylon check valve built into both the hot and cold side, I guess for idiots like me who put them in wrong in the first place!

I originally mounted mine in a high location far from the boiler without a heat trap. It would on occasion deliver scalding water for a few seconds before regulating the temp which is obviously not desirable. I doubt a heat trap would have worked on my system at the boiler coil anyway with copper piping. My cold water lines got mighty hot due to conduction with a 170+ boiler. Heat traps only stop convection.

Since I mounted mine in the wrong place the first time, I moved it lower than the boiler dhw outlet and changed the supply and mixed outlet piping to pex when I re-arranged the utility room, then put in a check valve to stop the thermal transfer to the cold side (which didn't work well because it was bronze), then realized the mixing valve was encrusted and pitted, with worn o-rings and just not doing its job well, then replaced the mixing valve, then replaced a section of the copper hot supply pipe to the mixing valve to stop the conduction from the boiler dhw.

Then, and only then, did I stop all undesirable thermal transfer.

(Now I am thinking about a bronze pump to maintain a higher mixed line temperature for quicker hot water at the tap-----NOT!)
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