Thermostatic mixing valve seized after < 3 years?


Old 07-31-16, 09:49 AM
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Thermostatic mixing valve seized after < 3 years?

We have a 3-year old house, and the tub in the master bath has never been as warm as every other fixture in the master or other bathrooms (100F vs. 120F). Now that we have some brief slices of free time as the kids get older, I wanted to fix this.

After doing some research, I looked for a mixing valve under the tub and found none, so went off in other directions until I noticed a mixing valve under the adjacent sink that was flowing to the tub.

It's a Honeywell AM-1 1070 (incidentally the only place they decided to install a mixing valve).

I unscrewed the cap and tried to turn it, no luck. Removed the cap and used increasingly larger pliers and a monkey wrench to try to turn the valve, but all I got were some nice brass shavings.

I'm guessing the valve has seized up. I'd love some perspective and suggestions on what to do, including:

1 - Is it reasonable for the valve to seize up after <3 years and very little use? We have very good water (Culligan-tested). Months ago we had some crud flowing through the hot water line that periodically clogged up the shower head, but that has disappeared.

2 - Am I trying to open the valve the wrong way? I'm trying to turn this brass cylinder that's about 3/16" diameter and 1/2" tall, with vertical grooves down the sides and a screw hole in the top. It won't turn either direction. I was able to rotate a black washer-type thing that is attached to it, which maybe has something do with a preset turning limit; it had no impact on the water temp.

3 - As a rank amateur, are there other options than calling in a plumber? I could theoretically turn off the water to the house, flush the lines, unscrew the hex nut(s) for the valve, take it apart, soak it in vinegar, brush it with an old toothbrush, put it back in, turn it (hopefully), and then put the water back on, but that's very hypothetical. Like, I might lose a part, put it back together wrong, brush so hard I break a spring or screw or something, in which case I'd have a busted valve and I believe an inoperable plumbing system until I can replace it (can't turn the house water back on if the valve is missing).

4 - I guesstimated to the wife $400 for the plumber. Is that reasonable? I'm assuming they could replace the valve, or just the entire setup.

Thanks for reading this and any advice you might have.
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Old 07-31-16, 10:46 AM
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Welcome to the forums.

I'm not the pro here but it looks the valve is attached with unions which means it should be easy to replace yourself.... if needed. The valve runs around $125.

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Old 07-31-16, 11:54 AM
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To adjust it, you loosen the screw on top, pull up on the black knob, turn the knob to adjust, and then push it back down and tighten the screw.

The guts can be replaced if necessary without replacing the whole valve.

Here's a link to the instruction sheet:

Good luck!
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