DHW Mixing Valve Scalding Temps

Kafox15

Hello,

I have a water heater that I keep set at 140F then use a Honeywell AM-1 series mixing valve to temper the output to ~115F. Generally, it works great, but I have been noticing an intermittent issue developing where the temp at our kitchen sink (one of the closest to the mixing valve) can get quite hotter than the set point for a few seconds(usually within the first 10-15 secs of running the tap) and then drop back down to the normal set point. Yesterday, I measured it at 135F for a few seconds before it dropped back to 115F. It's almost like the mixing valve is slow to react and lets hotter than usual mix water through for a few seconds before correcting itself. Obviously, this is a huge scald risk and I need to correct it.

Is the most likely culprit here a stuck or malfunctioning integral check valve on either the hot or cold inlet? Or is it more likely the internals of the valve itself need to be replaced?

Is it typical for these types of valves to fail in such a dangerous way? I would have hoped they would have had a safe failure mechanism built in if safe temperature couldn't be maintained.

Here are some pics of my install - in case there are any other potential concerns.

Thanks!

Intplm.

Your thoughts as to the check valve(s) not seating is worth a look. Open the valve at the unions, flush it with water, and see if that helps.

Larry Weingarten

Hi, In days past, it was recommended that a pipe loop style heat trap be installed between the heat source and mixing valve. This would keep the valve from seeing hot water all the time. Just a guess, but that approach might help you too.

Yours, Larry

Larry (from OSHA)

Hi, I have been using the same mixing valve as you for years. I have seen the same thing and found that exercising the valve after loosening the screw in the adjusting knob so you can turn the knob. It might be very hard to turn if not moved in a long time. turn on a faucet on full hot and move the mixing valve knob to the hot and then to the cold a few times. this usually takes care of the issue. the valve is rebuildable but just about the same cost to replace it if needed. they can get stuck from mineral buildup. also, how do you like the heat pump water heater?

Larry

Kafox15

Thanks all - I'll try these ideas from least to most invasive and report back! 

@Larry Weingarten could you please explain a little more how the heat trap works? I'm not sure I understand the concept. Are you implying that the constant presence of hot water could have somehow damaged the internal components of the valve?

@Larry (from OSHA) heat pump water heater is great. Do not regret it one bit. As long as you size it right and can put it in a location where the extra noise it makes won't bother you, It's a no brainier. I hear a lot of people say they don't work well in cold climates but we have had no issues in Massachusetts. 

hot_rod

If you have hard water, you will need to delime the valve occasionally, yearly, maybe less if you have really hard water

The scale precipitation increases with storage temperature, and of course the gallons that you use

Soak the entire valve in CLR overnight.
Some times having a second valve to swap in while you clean the scaled one, helps keep you in hot water

If it did work for a while, it is not a piping issue

I don’t see a recirc pump? Those can screw with thermostatic valves, called temperature creep.

Larry Weingarten

Hi @Kafox15 , @hot_rod basically said it, but in your case, the mixing valve will lime up faster with hot, hard water than cold, hard water. Additionally, corrosion processes speed up with heat. This means the valve will need more frequent service and will not last as long as the same valve in cooler water. I like to make heat traps at least six inches deep.

Yours, Larry

Mad Dog_2

I've seen these more modern Thermostatic mixing valves start "misbehaving" after they are installed 15-20 years.  We use them often.  That being said, the Holby Valves I come across in large commercial buildings are sometimes more than 50-60 years old  maybe older and they still hold down the fort.  Mad Dog 🐕 

Kafox15

Mad Dog_2 said:

I've seen these more modern Thermostatic mixing valves start "misbehaving" after they are installed 15-20 years.  We use them often.  That being said, the Holby Valves I come across in large commercial buildings are sometimes more than 50-60 years old  maybe older and they still hold down the fort.  Mad Dog 🐕 

Yikes this one is only 3 years old 

Mad Dog_2

They are sensitive.   Mad Dog 🐕 

hot_rod

If you remove it, disassemble it, you may find the problem
If it is scaled, that in not the valves fault. Switching brands would not change things

Caleffi has an electronic ball type  mix valve
Once a day it rotates the ball around to wipe scale

It has a control with functions for legionella protection, may be a bit much for a residential application 

Big Ed_4

The valve needs to be taking a part and cleaned out . It looks like there were issues with the sweats . Crap in the check valves they don't seat.....

Intplm.

Hey there @Kafox15
Is it too early to ask? Have you tried any of the suggestions offered here yet?

Kafox15

Big Ed_4 said:

The valve needs to be taking a part and cleaned out . It looks like there were issues with the sweats . Crap in the check valves they don't seat.....

Yea, there was a problem with the sweats. The problem is that I did them!
But I did remove the valve insert and check valves when soldering.

Intplm. said:

Hey there @Kafox15
Is it too early to ask? Have you tried any of the suggestions offered here yet?

So far, I have only had time to run the hot water and operate the valve back and forth a few times then set it back a safe temp. I would really like to have spare check valves and a rebuild kit before I take anything apart, just in case the original parts don't go back together.

I do appreciate everyone's great ideas and will update here when I can!

hot_rod

The checks really are not that critical. They are required if the valve is a 1070 listed device. The 1070, point of distribution valve does not need, or require check valves.

That may be a dual listed valve, does the handle indicate 1017 & 1070?

The checks don't usually present as a temperature fluctuation, more of a noise or reduced flow if the plug or fail. Or you melt them when you solder

I suspect the valve is scaled or a failed o-ring. Both maybe.

If you had a recic, it is good to have the checks.

Kafox15

@hot_rod it's ASSE 1017 - point of source but it did come with both check valves. 

I did remove the check valves before soldering.

 No recirc in this system

Is this the correct rebuild kit?
https://www.supplyhouse.com/Resideo-Braukmann-AM-1-025RP-AM-1-Repair-Kit-STD-and-R-Models

hot_rod

that is the correct valve for your applications  The repair kit looks correct also AM1 series

Kafox15

Just got the replacement kit and I'm a bit confused by the label. Says 100F-145F & 80F-180F but the valve I have is 70F-145F. 

I guess not a big deal for this application but am I missing something?

Kafox15

Well I went ahead and installed it. Looked the same as the one I took out. There was a decent amount of scale build up in the valve body and the hot side check valve was in rough shape. 

So I soaked the valve body and removed as much scale as I could and installed the new replacement kit and new check valves. Will see how it does.