Photo of an anti-scald tempering valve Hot Water Mixing Valve & Scald Protection Valve Inspections
Inspection points for hot water safety controls & valves

  • ANTI-SCALD VALVE INSPECTION - CONTENTS: inspection procedures & common defect lists for anti-scald valves, mixing valves, tempering valves & temperature compensating valves used on building plumbing systems to control hot water temperature
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Safety & functional inspection of anti scald valves & mixing valves.

This article describes key safety inspection points that should be examined when inspecting building hot water supply anti-scald protection and tempering valve or mixing valve or temperature compensating valve installations.

We discuss temperature or scalding safety, valve adjustment, and leak concerns at mixing valves, and we include manufacturer's instructions & warnings about mixing valve installation, safety, and periodic inspection & maintenance.

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How do we Inspect Mixing Valves or Anti-Scald or Tempering Valves

Tankless coil piping schematic example for a Crown heating boiler Safety First: are there temperature control devices installed on the building hot water supply system? In most jurisdiction scald protection is required for residential properties but it may not be specified by local codes for commercial properties.

When you find the temperature mixing or anti-scald device, check to see if the temperature controls properly set?

Check the temperature control settings on the device and where appropriate, actually measure hot water output temperature at the fixtures closest to hot water supply in order to assure that the mixing valve has been set to protect the building occupants from scalding.

Remember that while these valves may show a target temperature on the valve setting knob, the actual water temperature that comes out of a building faucet or tap will vary and may be hotter or cooler than the actual temperature set.

[Click to enlarge any image]

This is not precise lab-grade equipment capable of controlling water temperature precisely, and more, the length of pipe run between the hot water source and the building faucet or fixture will affect the temperature of water received there. A long run of un-insulated hot water pipe will deliver cooler water than a well-insulated water supply pipe of any length.

Leaks Second: See TANKLESS COIL / HOT WATER COIL LEAKS for a detailed discussion of how to recognize, evaluate, and repair leaks at tankless coils on heating boilers

At above left we illustrate the typical piping arrangement into and out of a tankless coil water heating system. Cold water is piped to an inlet marked "COLD" and building hot water supply piping is connected to the tankless coil outlet marked "HOT".

This tankless coil piping example from Crown Boilers indicates the use of a mixing valve or anti-scald valve right at the heating boiler. The company includes an interesting warning reading as follows [Quoting - Crown BDS Installation Manual]

WARNING: Thermostatic mixing valves are intended to increase the supply of hot water available from the coil. They are not intended to prevent a scald hazard.

Typical Hot Water Supply Temperature Control Valve Operating Range & Adjustment Settings

The following table is excerpted from ANTI SCALD VALVES / MIXING VALVES the home page for this topic:

Using the modern Watts Regulator Co. Series LF1170 / LFL1170 Hot Water Temperature Control Valve instructions as an example, these valves control water temperature in the following ranges:

Table of Hot Water Mixing Valve Output Temperatures [Watts Series LF1170 & LFL1170]

Hot Water Mixing Valve Model Cold Inlet Temperature Hot Inlet Temperature Factory Preset Outlet Temperature Output Temperature Adjustment Range Water supply pressure
Watts LF1170-M2
60-70 °F (16-21 °C )
140-145 °F
(60-63 °C)
120 °F (49 °C)
90-160 °F (32-71 °C)
45 psi (3.15 bar)
Watts LFL 1170-M2
90 °F (31 °C)
60-120 °F (16-49 °C)


The right-most "water supply pressure" number refers to the pressure at which these temperature readings will be expected for the mixing valves illustrated.

Source: "Instructions Series LF1170 and LFL1170 Hot Water Temperature Control Valves", Watts Regulator Co. (2013)

Best Practices Guide to Scald Protection for Bathrooms, Tubs, Showers

Look for the presence of anti-scald protection at the point of use of hot water in buildings and make the same inspection and tests of temperature we just cited above.

At the plumbing fixture outlet hot water temperature must be at or below the highest temperature allowed by local building codes. These temperature specifications vary by U.S. state and in Canada. Though 120 °F is a common upper temperature limit at the fixture, some states such as California specify a lower number (105 °F) and prison sytsems also have specific requirements.

See TABLE OF SCALDING TEMPERATURES & TIMES - where we explain how long it takes for hot water to cause a burn and where we cite regulations about water temperature control and anti-scalding requirements.

Watch out: it can be confusing listening to plumbers, home inspectors, and building supply sales staff who toss around terms like "mixing valve", "tempering valve", and "pressure-balancing valve" a bit loosely, all referring to ways to avoid scalding burns at plumbing fixtures, but not all working the same way.

There are several approaches to controlling hot water temperature to avoid scalding burns:

The high temperature limit control on the water heating device itself can be set to prevent scalding water from being produced.

Below at Table of Scalding Temperatures & Times we include a photo of a typical water heater label warning about scalding temperatures, implying that this option is one to consider.

A point of supply pressure balancing valve or automatic mixing valve (or a manual mixing valve) can be installed at or near the water heater, or at the tankless coil or other hot water source so that scald protection is provided even if the water heater is set to a high temperature.

This approach is sometimes used to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT.

This approach is discussed beginning at How Anti Scald Valves Work, and further reviewed by Steven Bliss at Water Pressure-Balancing Valves.

An temperature-sensing thermostatic mixing valve or anti-scald device can be installed at or near the water heating device so that even if the water heater is set to a high temperature (to obtain more total hot water as we discuss at Mix Valve Improves Hot Water Quantity and detail at HOT WATER IMPROVEMENT).

This approach is illustrated and explained at Built-in Fixture Anti-Scald Valves and is discussed further by Mr. Bliss at Thermostatic Mixing Valves. As noted in Chapter 6 of Best Practices Guide to Residential Construction:

There are many styles of mixer valves in tubs and showers, but all should have some sort of protection against scalding. The young and elderly are at greatest risk due to thinner skin and slower reaction times. More than 35,000 children, most under age six, are treated each year in emergency rooms for tap-water scald burns, according to the National Safe Kids Campaign.

A child exposed to 140°F water for as little as three seconds (see Table of Scalding Temperatures & Times) can sustain a third-degree burn requiring hospitalization and skin grafts. Although most scald burns occur in the kitchen, according to the Consumer Product Safety Commission, the most severe scald burns are caused by water flowing into the tub or shower. In response, many state and local codes now require antiscald protection in residential tubs and showers.

Many organizations advocate setting water heaters to no more than 120°F, which gives bathers significantly more time to move away or adjust the temperature before a burn occurs. While this strategy is helpful, it is not always reliable and can cause other problems:

Noncompliance: many homeowners turn the thermostats up to increase supply.

Water heater thermostats are often inaccurate. The ANSI standard for gas water heaters allows the temperature to vary by plus-or-minus 10°F.

Stacking effect: water at the top of a gas water heater can exceed the set point by as much as 30°F.

MIX VALVE SCALD PROTECTION, Best Practices, includes excerpts or adaptations from Chapter 6 of Best Practices Guide to Residential Construction, adapted courtesy of Wiley & Sons and written by Steven Bliss.

Inspect for the Presence of Point of Supply Water Pressure-Balancing Valves

Sparco tempering valve (C) Daniel FriedmanThese automatically adjust the water pressure to maintain the mix of hot and cold water to within 2°F to 3°F of where the user set the shower control.

If cold water is diverted to a flushing toilet or other appliance and the pressure drops, the valve automatically reduces the hot water flow proportionately to maintain the temperature.

If the cold water pressure plummets or stops altogether, the flow is reduced to a trickle.

To guard against someone accidentally turning the shower valve to scalding temperatures, these valves typically use a temperature limit stop that prevents the user from turning the shower control past a set point—typically set at or below 120°F.

A check valve is required on the cold water side to prevent backflow, and a hot-water expansion tank is recommended to prevent excessive pressure on the hot water side.

Figure 6-1: Accessible Kitchen Design Specs: accessible sink and dishwasher work centers (C) J Wiley S Bliss

The other type of thermostatic valve is built into some high-end showers (Figure 6-54). These allow the user to set the temperature on a dial when showering.

The unit will compensate for changes in either pressure or temperature to maintain a constant delivery temperature and flow rate.

If the cold water fails or the tempered water is still too hot for any reason, the unit will shut off the flow.

As with the pressure-balancing valve, the installer sets a temperature limit stop to prevent the user from turning the shower control to scalding temperatures.

We illustrate this approach as it is installed in a modern bathroom in Molde, Norway at Built-in Fixture Anti-Scald Valves.

Retrofits to Avoid Scalding Burns at Plumbing Fixtures

In retrofits, point-of-use devices can be installed by a plumber or homeowner to limit water temperatures to 120°F. These include antiscald showerheads, as well as point-of-use devices that fit into individual plumbing fixtures, such as showerheads and bath and sink faucets.

For example, MemrySafe and ScaldShield (Antiscald Inc.) are inexpensive retrofit devices that reduce the water flow to less than 1/4 gallon per minute when the water temperature at the faucet or showerhead exceeds 120°F. These devices do not regulate temperature or pressure, but do offer protection against serious burns.

Mixing Valve Installation Safety Warnings From the Manufacturers

Watch out: read the installation instructions from the manufacturer of the product you are installing, both to make sure it's installed properly and thus will work as expected, and also so that you understand what to expect by way of hot water temperature control the product handles.

At TANKLESS COIL INSTALLATION PROCEDURE where we recommend the use of mixing valves we quote this warning from the Crown Boiler Company:

WARNING: Thermostatic mixing valves are intended to increase the supply of hot water available from the coil. They are not intended to prevent a scald hazard.

Similarly, the Watts Regulator Company's instructions for the installation of the Series LF1170 & LFL 1170 Hot Water Temperature Control Valves includes this warning: [Bold font is our emphasis]


This Hot Water Master Tempering Valves cannot be used for tempering water temperature at fixtures. Severe bodily injury (i.e., scalding or chilling) and/or death may result depending upon system water pressure changes and/or supply water temperature changes. ASSE standard 1016, 1069 or 1070 listed devices should be used at fixtures to prevent possible injury.

These Hot Water Tempering Valves are designed to be installed at or near the boiler or water heater. They are not designed to compensate for system pressure fluctuations and should not be used where ASSE standard 1016, 1069 or 1070 devices are required. These valves should never be used to provide “anti-scald” or “anti-chill” service.

The components of the system must be of materials with a construction capable of withstanding the high limit output temperatures of the water heating source. - Watts (2013)

Other Mixing Valve Warnings - using Watts instructions as an example, include :

Need for Periodic Inspection and Yearly Maintenance: Periodic inspection and yearly maintenance by a licensed contractor is required. Corrosive water conditions, temperatures over 200°F, unauthorized adjustments or repair could render the valve ineffective for service intended. Regular checking and cleaning of the valve’s internal components and check stops helps assure maximum life and proper product function. Frequency of cleaning and inspection depends upon local water conditions. 

Building code compliance for mixing valves: You are required to consult the local building and plumbing codes prior to installation. If the information in this manual is not consistent with local building or plumbing codes, the local codes should be followed. Inquire with governing authorities for additional local requirements. ... Valve should be installed and adjusted by a licensed contractor in accordance with local codes and ordinances. Further, this valve should be installed in a location where it is accessible for cleaning, service or adjustment. - Watts (2013)

Anti-Scald & Hot Water Safety Articles


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