mixing valve

oreo123

Wall hung combi boiler 150k btu input. Domestic hot water output at 2.3 gpm is 139 F. Cannot get it higher on its software.

Mixing valve max'd out to hottest output temp is 116F. I need 123-125F.

Is there a mixing valve, lead free, copper press that will work in this application?

Larry Weingarten

Hi, What kind of valve do you have in place now? Is it a 1070, or 1017, or? Also, where is it relative to your heater?

Yours, Larry

oreo123

calefi mixing valve. Located 2 feet to the side of the combi. 3/4 copper press.

Two identical boilers next to this one. Those mixing valves also set at highest temp and only get 123F output.

I reduced the cold water into the mixing valve. Probably 25 percent of the volume in and got the 116 F. If the cold water is fully open then the output temp drops to 110F.

I question if there is a mix valve that would have input of 138 and output of 125.

Will contact inspector tomorrow to see if its mandatory to have a mix valve on a combi with a max output of 138F, The combi software will allow me to program it down to 125.

oreo123

Caleffi CLF521516AC
Mxg Vlv Mixcal Adj Thm 3w W/ga Inl Chk

mattmia2

what temp do you measure at the outlet of the boiler?

oreo123

Boiler output of domestic hot water is 138 and sometimes down to 136 Fahrenheit

hot_rod

The hot water supply to the valve needs to be around 25 degrees warmer than the mixed temperature that you desire, for the valve to mix properly.
Any mixing valve with a ASSE 1070 listing will be limited to 120 mix.
The 521 should be a 1017.

Try raising the hot water 5 or 10 degrees

oreo123

if combi boiler maxs out at 140 degrees input to mixing valve - what else can be done? We need 123 output from mixing valve. Current mix valve is 1017 mod 521.

All boilers are in basement. Each boiler supplies an apartment above on first, second, third floor. Heat and domestic hot water.

Supply house rep is out in morning.

Plumbing inspector wants mixing valve to avoid scalding when it goes from heating to domestic production.

mattmia2

Serve the equipment that requires 125 degree water separately from the fixtures that require scald protection?

mattmia2

Caleffi makes a motorized mixing valve for dhw that can handle a smaller differential but it is expensive.

Jean-David Beyer

Serve the equipment that requires 125 degree water separately from the fixtures that require scald protection?

I would like to do that, but in my house, it is practically impossible. Most of the piping is in the slab upon which the house is built, as are the radiant heating pipes. To run a separate line from the indirect hot water outlet to the dishwasher would cost many many thousands of dollars. As it is, I can get about 122F or so from the mixing valve, but by the time it gets to the dishwasher, I cannot get it much over 110F no matter how long I run it. So the electric heater in the dishwasher has to get it up the rest of the way to 165F for the final rinse. Now I am not supposed to put over 120F into the dishwasher, but I would like to be able to do it.

I do have a Taco recirculating system in there, but my usage is so irregular that their SmartPlug controller cannot manage it. And even when works, it does not work because it runs 5 minutes on and 10 minutes, off and I cannot get the temperature up to its maximum in so short a time.

mattmia2

You could also distribute at the higher temp and add mixing valves at each fixture(or group of fixtures) that the code requires anti scald protection.

hot_rod

Sounds like the piping in the slab is the bigger issue. Can you just run the Combi DHW at 125- 130? Account for the temperature drop in the slab. Why do you need the mix valve? The lower you run the DHW the higher the gpm rate on instantaneous heaters.

If you want additional protection at the sink, add a 1070 valve at the point of use.

oreo123

situation resolved Boiler company came out. Looked at all three boilers and said it was a good install. Whew..

Boiler company rep asked about shower volume. And if a low flow shower head. Yes, shower head was installed 2 years ago and low flow. Cannot remember exactly but it was around 1 point something gal per min. Standard symons shower valve.

I went into apt, ran shower hot only, saw it go hot and then a couple of minutes later ran cold. Turned on hot water bath faucet and it stayed hot.

Was told that if there is a heat exchanger and the flow is too low it shuts off the hot domestic output for a few seconds and there is the rush of cold water. In my state they are pushing low flow heads and combi high efficiency boilers. My take is we cannot have both without having issues. Boiler manufacturer said that they have seen this issue many times before.

Next: Local inspector wants mixing valves on combis. The reason being say its the middle of winter and boiler is running for heat. Next someone takes a shower so boiler shifts to domestic. If boiler was up at 180 F. and it shifts quickly to domestic that very hot water will cause a spike and a mixing valve will prevent a burn.

hot_rod

What's odd is the combi and tankless manufacturers pushed for and received an ASSE standard indication they can control output temperatures as accurately as a mixing valve, hense no mixer should be needed or required on those heaters.
That being said, I'm not sure I have seen any brands promoting that they meet that new standard? It is not a replacement for a POU valve which most single handle shower valves have built in.

For tankless and combis you want a fast acting mix valve, and one that is accurate down to 1/2 gpm flow. We designed a thermostatic mix valve specifically for that use as the majority of Europe, really the rest of the world uses tankless and combi predominantly. Other than solar, it's rare to see a tank style DHW device.

Lance

If "Hot Rod" said it. Its golden!

oreo123

" We designed a thermostatic mix valve specifically for that use as the majority of Europe".

These boilers are made in Europe. I will try to snap a pix of the part today and see if there are numbers on it. And I will try to see if its ASSE approved.

mattmia2

If the flow is too low for that particular valve it also will not work correctly.

oreo123

Matt. Yes that was the issue. Too low water flow through water saving shower head. Yesterday I was advised to keep a min of 2 gpm flowing to have boiler stay in hot domestic mode.

mattmia2

There is a way to cascade 2 valves with different CV ratings so that the lower flow uses a lower CV valve that can regulate at the lower flow. @hot_rod I think can tell you how to do that.

hot_rod

oreo123 said:

Matt. Yes that was the issue. Too low water flow through water saving shower head. Yesterday I was advised to keep a min of 2 gpm flowing to have boiler stay in hot domestic mode.

2 gpm seems awful high for a residential combi boiler to activate and stay in DHW mode. You would need two or three faucets flowing to maintain that gpm. That doesn't sound correct? Maybe the boiler side needs 2 gpm. I think they use a small 4X8, 8 plate HX that requires a high A side flow to give you the DHW they indicate. That may be how the 2 gpm enters into the equation so the boiler has adequate flow.

The flow switches to trigger combi and tankless are .5 or lower gpm. Granted you will hear the boiler ramping up and down to maintain that low flow, but every combi I have owned works fine with just a small hand sink .5 gpm draw. Although you may notice a small temperature change under very low flow rates, if the boiler cycles off on high limit, and re-fires.

Its a real crap shoot out there as to where the codes are being enforced for thermostatic mix valves. Even in areas where they are code required, enforcement is spotty.
Personally, if the unit can maintain a + or - 2° output, as many claim,I would not add a mix valve. You take a pressure drop, and add a maintenance sensitive valve, especially in hard water areas, most of the US of A

This 520 valve is somewhat unique in it angle pattern, 18 degree delta, .5 gpm accuracy and 100% shutoff if you lose hot or cold flow. This valve or another with a similar spec should work fine with instant type DHW units.

When performance drops off on a combi, most assume the B side, DHW side is fouled, but I have seen the A side foul on systems with crappy water quality. Or non barrier tube systems. And a scaled mix valve will present unstable temperature at the faucet.

mattmia2

Wait, is it that the flow through the boiler is too low to keep it calling or is it that the flow through the selected mixing valve is too low for it to work correctly?

If the output of the boiler is hot enough and the cold water is relatively warm i could see where there would be so little flow because little hot water is required in the mix that it wouldn't keep the boiler calling for dhw.