High system pressure cause mixing valve failure?

RascalOrnery

I've had 3 mixing valve failures in less than 2 years which come off my tankless coil from my boiler.

The coil is only 2 years old and I am on city water, but the pressure is over 100 psi. I'm looking into a pressure reducing valve to install since my house probably could only improve by having one.

I hope to take off the current mixing valve and do an analysis as to what is wrong, previously I had o rings ripped that I replaced and it fixed the problem, then I had a failure again in a few months so I stuck on a spare mixing valve I had (AM-1 I believe) and that lasted me several months but now is doing the same things as before (hot water at spigot drops as boiler temp drops), like the valve is just doing a direct proportional mix. (pressure is fine)

Do the internals have temperature component limitations that are concerning for temps getting up to 190-195? Sometimes my boiler can coast that high.

My suspicion is that the high pressure is causing undo issues for the mixing valve? It doesn't seem that a partially blocked coil is likely since it's age and being on city water, however I am getting the water quality checked and plan on installing some kind of filter to protect myself against such nonsense, what would I look for in my water that would cause scaling in my coil?

Please advise! I'm open to learning!

If I find my coil is blocked I think I'll be looking into an indirect for the future, anyone care to post some research links?

pecmsg

100 PSI is extreme. Install a reducing valve.

Jamie Hall

Actually it is possible that the very high pressure could cause problems with the mixing valves — though I think it is unlikely. It is also quite possible that the mixing valve is operating outside it's comfort zone — if your hot water input is getting up as high as you say, and you are mixing down to 120 or so (I presume this is for domestic hot water), the hot side will be almost closed, and that can lead to problems.

The only thing that will cause scaling in the coil is excessive hardness, but the water have to be really hard to do much in only two years. A filter won't help that.

Do get a pressure reducing valve installed. However, also be aware that with a pressure reducing valve you will also need a small expansion tank on the domestic hot water. I you are using the coil, it needn't be large — but it is needed.

hot_rod

how high is your pressure, do you have a PRV?
A thermal expansion tank?

Most valves are rated to 195F, 150 static pressure , 75 psi dynamic operating pressure.

High pressure, hard water, high operating temperature, excessive chlorine or chloramines, add stress to the valves.

Unequal pressure between hot and cold will cause them to shut down. That can happen if the coil is badly scaled, the hot pressure drops, as you start flowing.

Most valves have a 2:1 pressure ratio, if you have 60 psi incoming and the hot drops to 30, that will be an issue

So check incoming pressure over a week with a lazy hand gauge. 60 psi is plenty, 80 is too high

Thermostatic valves can be high maintenance in hard, high temperature water. You may need to clean or descale every 6 months

RascalOrnery

Thanks for the quick response guys! I do have a small expansion tank that I put in on the cold side for the domestic hot water to help relieve water hammer. With a system PRV is that sufficient or should it be after the mixing valve on the side where the hot water goes to the fixtures?

I borrowed a gauge from a friend and I can't remember if the system pressure was 120 or 130 or something…but it was high. FYI while this may seem crazy, the area I live in a think is rife with this sort of thing, two other friends who bought houses did not have low water cutoffs on their boilers or PRV's in there homes. The house I grew up in did not even have a mixing/tempering valve, it was just "don't get burnt" and several people I know who have a boiler didn't know what I was talking about when I said about a mixing valve. :D so I am ahead of it! This house is 100 years old and probably has had water for most of that time, and there is pretty much just straight piping with barely any shut off valves, so me just getting to it as the recent owner…is rather embarrasing!

Is it likely for my city water to be hard? I though hard/soft and such was usually a well water discussion?

What items fail on these type of mixing valves in high pressure high temperature situations? Seals mainly or do you think the check valves get slammed around or o-rings get shredded from the stress?

hot_rod

45-60 psi is plenty for residential systems. Above that all the plumbing valves and fixtures are stressed. Excessive pressure is more prone to water hammer also.

Mainline pressure above 150 psi should use a two stage PRV. First stage to 100 psi, second to 45-50.

Water hardness test kits are cheap. The color changing strips are close enough. Few places in the U.S. have soft water.

Excessive pressure hammers seals, seats, o rings etc. A PRV is not an expensive protection device.

Ironman

Caleffi’s angle mixing valve is a much better product than the Honeywell. We quit using those some years back because of the high failure rate.

RascalOrnery

This is the one I was looking at:

https://www.supplyhouse.com/Caleffi-535351HA-3-4-NPTF-Pressure-Reducing-Valve-w-Gauge-Low-Lead-Pre-adjustable

Thanks guys! My brother in law told me our water authority posts the water properties so I should be able to look at that for starters, looks like I'm on the fringe of slightly and moderately hard area

hot_rod

excellent PRV, easy to service, high flow rate

Also when next you replace the mixer we still offer a solar version, higher temperature rating rating. It has different polymers inside for extreme temperature use. Although limit the hot temperature as much as you can.

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EBEBRATT-Ed

PRV and expansion tank as others mentioned above.

hot_rod

the 520 anglemix is a valve designed specifically for tankless water heaters. It responds very quickly

Notice two important numbers, on the two valves maximum temperature, and the minimum flow required

If you use a lot of low flow faucets, or shower heads, the 520 is a better valve. But your high temperatures 195 plus are concerning

The solar valve handles the temperature better, but needs more flow to be stable. With a small sink draw less than 1 gpm, the temperature will vary as the valve “hunts”

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RascalOrnery

Thanks you all so much, especially @hot_rod for the helpful links and info!

Intplm.

And if you're still concerned about the quality of your water, your water utility will send you a water quality report at your request. Some may even post them on line.

RascalOrnery

Yes, I did find it, thank you!