Thermostatic mixing valve... often found at water heater & under vanity sinks in MB.

We’ve been explaining to a lot clients what the mixing valves installed at the water heater and/or under the (typically) MB vanity sink are intended for, they are almost never correctly adjusted (in our area). Recently I have seen some Facebook home inspector group posts inquiring about mixing valves. Here is a few links for those wishing to research about water mixing valves:

Anti-scald valves, tempering valves, mixing valves on hot water systems and at plumbing fixtures
Thermostatic mixing valve - Wikipedia

This is the narrative we include when we don’t find a mixing valve installed at the water heater.

There did not appear to be a temperature mixing valve installed at the water heater. These mixing valves are typically installed to allow the water heater to be operated at or above 140 degrees F to kill bacteria such as Legionella. Legionella is an aquatic bacteria that thrives in warm water environments, and can cause Legionnaires Disease. It is commonly found in potable water supplies, hot tubs, cooling towers, fountains, swimming pools, etc. and multiplies in warm conditions especially between 68 – 122 °F. The Legionella bacteria can spread to humans when breathed in. We recommend installing a mixing valve and setting the temperature of the water heater to 140 degrees F and adjusting the mixing valve so that the water delivered to the home is in the generally acceptable range of 110 to 120 degrees F to prevent scalding hazards while protecting against Legionella. Also note that most electric water heaters have energized electrical components at the temperature adjustment area and should be adjusted by a qualified person in accordance with the water heater manual installation/operating instructions.

And this is what I put in my reports.

Very good information. Thanks guys.

understand & prevent scalding

I’ve never seen one.

Part of the 2012 iteration of the IRC. You should start seeing them on new construction as the standard is adopted.

I have begun to see these on new construction/ 11 month warranty inspections. Homeowners are not happy because the tub that they are usually attached to doesn’t get hot enough to take a bath in.

They are adjustable. I always check temp on tubs equipped with them.

Several homeowners around here have had them removed (bypassed) after moving in, for that reason. They have a preset max temp.

I’ve seen hundreds of them the last few years…one was adjusted correctly. Today’s water heater was set above 140 but the mixing valve was not correctly adjusted. Some of the plumbers around here put a sticker right on the side that tells how to set the tank and the valve… but still don’t do it.