Domestic hot water mixing valve not working

[muncybob]

Hot water from the boiler coil is hot enough to cause a burn. I think it has been like this from day one of the boiler install but I could never get the installer back to correct the problem. A plumber looked at the situation and said the valve is not in the right place. Does it make a difference where the valve is installed? The coil is at the very top/rear of the boiler and the mixing valve is at the same height and apprx. 1 foot from the coil inlet/outlet.

Had another person say he thinks it's just a defective mixing valve and possibly when it was soldered in a piece of solder got into the vale itself and that's why it has been defective?

 

[peakbagger]

For some reason years ago the guy who sold me my valve insisted that it had to be installed lower than the coil outlet so my piping makes a big loop down next to my boiler. I have changed out a few elements over the years for others so they can go bad. The Taco versions are usually on the shelf at Home Depot, I have never seen just the element for sale so I just buy the entire valve and throw away the body which is soldered in and replace the guts.

If I had to guess why installing it lower than the coil outlet it would be to having the valve exposed to the high temp from the coil 24/7, by mounting it lower the heat will stay trapped in the piping in the coil and the valve will see somewhat cooler temps being mounted lower? This would be a long term issue rather than what looks like something that is happening right away.

By the way, these mixing valves are not intended to be substitute for an anti scald valve for each fixture. The older style mixing valves can fail in any position why an antiscald valve is usually set up to fail closed to prevent scalding. I have a Honeywell mixing valve with antiscald protection on my SHW system. I also have a rebuild kit just in case.

 

[Bob Rohr]

What brand and model do you have? The valve should have an ASSE listing number 1017 to assure it is a safe, accurate valve.

The valve should "fail cold"

Thermostatic mixing valves do require maintenance and cleaning of hard water deposit, in some jobs every six months or so. Service intervals depend on hardness of your water, hot water temperature supplied to the valve, and how many gallons you run through it.

Usually soaking them in vinegar will remove hard water deposits, most have rebuild kits if the 0 rings get damaged.

There is also a valve with a ASSE 1070 listing. This is intended to be use at the point of use, or fixture. It is limited to 120F max. setting for final protection.

A few other points, the hot supply needs to be at least 25 degrees warmer than the mixed temperature. Check valves are sometimes needed to keep the H&C from crossing over, most valves offer the connections with checks.

 

[Fred61]

It's been34 years since I installed one of these and if I remember correctly the manuals state that the valve must be installed lower than the output of the coil. In other words, angle down or elbow down a few inches before installing the valve. Over the years I have seen very few of these installed in such a manner. Bob R knows more about this than I do though.
These valves lead a rough life. with new hot water flowing through them. If your water is hard or just moderately on the hard side the heat will accelerate the deposit of calcium on the surfaces. Same goes for slightly acidic water which many municipal water systems have that will corrode the inner components. Heat accelerates any chemical reaction.

 

[Seasoned Oak]

Iv had to replace mine every few years at over $100 . SInce then i got a whole house water filter ,seems a lot of dirt gets into the municipal water supply. Helps with all my furnace controls, pressure valves,toilet regulators ect ect

 

[Bob Rohr]

Hard water is tough on all the plumbing. Here is a simple test for hardness.
Really an ion exchange water softener is the best way to lower the hardness. De-mineralizer filters may do some good but will need to be replaced, they cannot be backwashed when plugged with hard water ions.

http://www.wikihow.com/Determine-if-You-Have-Hard-Water

We get valves returned looking like this and the owner wants a warranty.