FAQs about Anti-Scald protection for water heaters.

In these hot water temperature control articles we explain how to buy, install, adjust and inspect anti-scald equipment to prevent hot water burns. We explain what a mixing valve, tempering valve, or anti-scald valve is, where and why these valves are installed on hot water systems, and how they work.

FAQS on Mixing Valves / Anti Scald Valves on Hot Water Systems

These questions & answers about the requirement for anti-scald or anti-burn valves at hot water heaters and their installation, inspection, adjustment or repair were posted originally at ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES- be sure you review that information.

Photo: a Sparco anti-scald valve or tempering valve installed at a hydronic heating boiler. Other texts refer to these safety controls as mixing valves or compensating valves or temperature compensating valves.

[Click to enlarge any image]

On 2017-11-28 by Mod - use a mixing valve with indirect hot water heater?

Any water heater that can be or is set above scalding should use a mixing valve or anti-scald valve. That includes indirect water heaters.

On 2017-11-28 by Anthony

Is it wise to use a mixing valve with indirect hot water heater?

On 2017-10-04 by mod

If the adjustable knob or handle on your mixing valve is jammed I suspect it's due to corrosion or scale formation - and you may need to de-scale or replace the valve. But check first to see if your model includes a lock nut or screw to prevent tampering.

On 2017-10-04 by Anonymous

The handle on my mixing valve will not turn why is that

On 2017-02-05 1 by Jeff Salmon - TMVs in the UK

have just had what should purportedly have been a high class refurbishment/conversion ( costing some £750K) in an existing building. In one of the baths and at all sinks through the property there are no TMV valves. The builder (much has gone wrong with the plumbing) is now relying that under Water Regulaitions TMV's only have to be fitted in New Builds. Indeed I have checked this and this is correct.

However, the contractors DID place one TMV on top of the water cylinder which has made no difference at all to the generally heat of the water throughout the apartment.

My question in the circumstances (I don't want to be accused of asking a leading question) is what would the majority of good quality contractors do whilst working on a high quality refurbishment/conversion and not a New Build. Would they put TMV's everywhere or use the Water Regulation Rules not to install TMV's. thank you and I look forward to receiving your responses.

On 2016-05-10 by (mod) -

Anne,

I appreciate your frustration but can't second guess what the plumber was told, heard, or thought nor the order of her thoughts. For example if someone gave me to think that the hot water complaint was for just one bath shower I'd focus there; if the complaint was that none of the fixtures had water that was hot enough I'd start at the water heater and mixing valve.

On 2016-05-10 by Anne

We bought a house that had been renovated top to bottom 4 years earlier. Large beautiful master bath just couldn't get water as hot as I liked, ever. Called a plumber and he replaced a shower valve. No chance. Another day, he replaced the bath valve. Nothing. Finally, he changed the mixing valve. The bill for the first valve (changed unnecessarily) came to over $600.

Part of the time he left us with no water in the house at all while he got the part and did a quick emergency job. Wouldn't a master plumber have thought of the mixing valve before charging for two days and two perfectly good valves?

On 2016-04-12 by (mod) -

Anon:

Before blaming the heater I'd get some diagnosis of what's wrong.

Do not remove the anti-scald valve as doing so can badly burn someone now or someone later.

I can't make very specific suggestions as I don't know what sort of heater is installed, but you might start by reviewing the heater's temp settings and anti-scald valve settings.

I'd also be alert for a partly-closed valve or a bad plumbing job that pushed so much solder into a joint that it's partly blocked.

On 2016-04-09 by Anonymous

How do I remove an anti-scald device on my new hot water heater? We just bought a new heater and had it installed, now I wish we hadn't! We cannot get enough hot water or pressure. We have no kids and are both ADULTS that have enjoyed our hot water for years with not a scald on us. We want our water the way we want our water. Please help!

On 2016-02-25 by Sarah

We have to have mixer valves fitted to all sinks in our residential care home. Recently a mixer valve failed and forced hot water into our cold water tank, when our maintenance manager did his monthly temp. check of the cold water tanks the water was hot and the tank was mis-shappen. This has necessitated us having to have the cold water tank replaced.

This is the second time this has happened. How often should we replace mixer valves? Does this happen often is is there another cause?

On 2016-01-03 by (mod) -

Ian

In the article above I have added details about adjusting the Pfister tub and shower valve temperature.

On 2016-01-03 by ian paul

So I have a Pfister with the anti scald valve in my shower. It's the only anti scald valve in my house and I can never take a really warm shower and it's killing me! Is there any modification I can do to get it warmer because adjusting it doesn't work

On 2015-12-12 by (mod) - anti-scald devices or protection is required by law in many communities

Duda:

Is what legal? Scaldig. No. Or maybe - depending on where you live.

Check with your local building department to see what anti-scald rules they enforce for rentals.

see HOT WATER ANTI-SCALD REGULATIONS

On 2015-12-10 by Duda

Sorry Multi-Family Apt. in Saint Peterssburg, FL. No anti scald on water!

Is This Legal? Get scalded quite often!

Question: Watts tempering valve problems

I had the inside of my Watts tempering valve replaced but I still have problems. In warmer weather the water is very hot but after several minutes it becomes warm. Someone said I should replace the hosing as it has a disc and spring that can malfunction. Any answers? - Ed 12/8/11

Reply:

Ed, sometimes hot water rises into the hot water piping above the water heater by natural convection - it depends on piping arrangements. There are special check valves sold to prevent that trouble. I'd replace the valve rather than take a chance on an improper repair that could scald someone.

Question: how do hotels keep hot water safe and instantly available?

How do hotels insure that water stays at proper temperature and are they subject to inspections - Dawn 5/27/12

Reply:

Dawn, some hotels use a system that continuously circulates hot water through a piping loop throughout the building.

By that means, when you turn on hot water at the sink, hot water is right there by the sink, in the wall or floor, having only to rise up through a very short section of piping en route to the faucet. Details of using a hot water circulating loop for instant hot water are provided at

HOT WATER DELIVERY SPEED UP

see article links at page top or left

Question: hot water scalding burn report

i was recently burned in a fast food restaurant using a men's room urinal and was told this happens when the kit sink is on it forces scalding water to the urinal how is this possible - Ken 6/18/12

Reply:

Ken, sorry to read that you were burned. In my OPINION there is absolutely no proper plumbing hook-up that would ever send scalding or even hot water to supply a urinal. It sounds like a plumbing mistake and most likely improper installation.

Question: hot water comes out of the cold water tap then turns cold

We have the problem that our *cold* tap water starts out hot, and only turns cold after running for a minute or so. (This is an apartment with its own 60 gallon gas water heater.) Could this be related to the anti-scald valve? - Henning Schulzrinne 9/11/12

Reply:

Henning,

I suspect that the hot and cold water lines must be quite close or even touching right at the fixture.

Question:

We have a 6 unit apartment building and a tenant is experiencing very hot then cold showers after adjust it to a warm shower. It is a newer hot water heater. How do we provide consistent water temperatures for our tenants? - Joann 9/27/12

Reply:

Install a tempering or mixing valve as discussed in these articles. Either at the shower or at the hot water source.

Question: I want to replace an old mixing valve on a Hoval Dulyte boiler

I am looking for a "mixing valve" for an old Hoval Dulyte boiler. It is German made and about 25 years old.

The old valve was a T300, I believe, and it is now malfunctioning. I need to find a compatible part. The motor is mounted on a 3-way fitting measuring 1.25". If you have such a part, on any advice, it would be greatly appreciated. You can contact me by phone 860-267-6128 or email drivebyduck@yahoo.com
Thank you,
Maureen Heidtmann 12/3/12

Reply:

Maureen, you may be better off removing the old device, sealing its mounting openings, and installing a modern, readily-available anti-scald valve.

Question: Moen single lever shower control, irregular hot water, how do I avoid temperature swings

I have a shower with a Moen single lever control. I do not have a anti-scalding valve on the hot water heater. I experience significant and frequent swings in the temperature of the water from this shower if any water is being used anywhere else in the house including the basement washing machine (my shower is on the second floor). what would you recommend - John Pratapas 12/6/12

Reply:

John,

I've found that temperature swings can be a real hassle, even dangerous; the best protection is to install an anti-scald valve right at the device or shower, though it's a mess, meaning tear out and re-plumb what's there.

IF you can get to the back of the shower wall from the other side (less of a hassle) you may be able to install a separate mixing valve there instead - cheaper, less demo.

I'd suggest installing a mix valve right at the water heater as a whole-house solution - as until this month I thought that was the best solution.

But working on an article (just finishing up today - see TANKLESS WATER HEATER INSTALLATION) on how to install a tankless water heater I found that building piping routing and layout can cause some odd temperature behavior depending on system water pressure and type of hot water heater in use.

So those are the two choices.

Question: calcuim build-up clogs anti scald valve?

(Dec 26, 2012) Natalie said:
We have a townhouse with a tankless boiler which is supposed to provide up to 12 gpm hot water.

There is a Honeywell thermostatic mixing valve installed right off this main hot water line, assumably doing its job of tempering the whole-house hot water. The issue is that even with one extra faucet or shower on, somebody using hot water will get lukewarm, or even pure cold, water.

If none of these faucets or showerheads use more than 2.5 gpm, how come we can never use more than one warm or hot water outlet at a time? It is a real nuisance, and the tenant is complaining of cold showers.

(Jan 26, 2013) Walt , Cen NJ said:
not sure this is a Mx/Vlv problem , but the hot water get kooler after awhile in the shower, I replaced the Mx/Vlv , once , and it was good for awhile , steady hot water. We do get heavy clacium (?) buildups on shower heads etc, could the valve be getting clogged?,

Reply:

Walt, Cen NJ

If hot water temperature drops that's not likely to be due to the mixing valve, more likely due to the water supply or supply piping.

Question: override the mixing valve?

(Mar 29, 2013) Alice said:
Is it possible to install something to override a mixing valve from the apartment below? The landlord in the apartment below me has been using a mixing valve to prevent me from getting adequate hot water. I've been contacting the landlord and suing him and nothing has come of it.

Reply:

Alice,

I'm not sure how we could have a plumbing fixture that is downstream from a mixing valve that could override it. That's because all water getting past the mixing valve will be tempered or adjusted to the temperature set by the valve. To make downstream water hotter again one would have to add a heat source.

Question: repair an anti-scald valve

(Mar 13, 2014) ken said:
Anti-scald valve on hot water heater leaking when water is used. Leaks from cold side connection and from brass plug on bottom. Seems a simple fix but is a special thread sealer required for hot water? And, is fix as simple as it seems?

Reply:

Ken,

A fix often sounds trivial but in the execution runs into snafu's. As long as you're careful that no pipe sealant is placed where it can enter the valve body, thread sealant or teflon tape should be ok.

I took a look at the Watts anti scald valve installation instructions again - I don't see any discussion of valve disassembly, repair, nor use of sealants except the following;

Period Inspection/Maintenance of Anti Scald Valve

This valve requires periodic inspection and verification of the outlet temperature by a licensed contractor.

Corrosive water conditions, hot inlet water temperature over 200°F (93°C), unauthorized adjustments or repairs could render the valve ineffective for its intended service. Regular cleaning and checking of thermostat assembly helps to maximize valve life and mixing function. Frequency of cleaning depends on local water conditions.

Honeywell's Sparcomix tempering valve instructions include detailed procedures for disassembly and cleaning of the valve.

And most of these valves have a replacable internal element.

None of the instructions I reviewed addressed sealants.

Question: water is sometimes scalding

(Mar 19, 2014) Brian said:
I installed a 'T' to mix hot and cold at my bathroom sink so that warm water comes out of the hot side of the faucet. I capped the cold side.

My water is sometimes perfect but can quickly change to scalding. Is a mixing valve different then just a 'T'? I thought maybe it was because the 'T' was connected to the hot water but I tried it on the cold side with the same result.

It doesnt matter if another fixture was being used at the same time as it has turned scalding with just the one sink running. Any insight or ideas would be great! Thanks

Reply:

Brian,
An automatic tempering or mixing valve monitors the outgoing water temperature and holds it with a narrow range around the desired temperature setting.

A manual mixing valve such as your arrangement will permit water that is too hot or too cold depending on variations in the incoming cold and hot water temperatures. The best you can do with a manual-only mixing valve is to set it to use enough cold that the outgoing mixed water is *never* scalding. That means at times it'll be cooler than you'd like.

Question: Ever Hot side arm coil is erratic, trying a mixing valve

(Apr 29, 2014) Alex Brown said:
We have a EverHot side arm water heater which has been very erratic ever since installation. At first the water is hot, then sharply falls off to a tepid temperature. We've spent $$$$$ on trying to get this diagnosed. The latest suggestion is the mixing value (manual style) is for residential use. It the EverHot is commercial grade. Our Hv tech suggested we install a commercial grade mixing valve. Any ideas or suggestions would be appreciated. Your article was so helpful. Thqnks

Reply:

Alex, I'd be glad to look into the question.

Of course I'm inclined to defer to the onsite expert but I do have some questions.

Is there any more model informationabou the EverHot?
Also if you want to send me some sharp photos of the system and piping and valve arrangement that might invite comment as well. Use our CONTACT link.

I'd like the same info on the mixing valve: brand, model, photos.

How is this system being used: is this a commercial rather than residential application? At higher volumes?

Question:

(June 9, 2014) Bill Garwood ACI said:
I see multiple sinks with a mixing valve only under one of them. How does this work?

(Jan 9, 2015) Anonymous said:
I have a hot water heater that I have already changed the mixing valve on 4 times and I still cant keep the hot water regulated,it is still spiking, one time it will stay at 110 degrees and you go back later to check the temp and it is back up to 126 degrees

(Jan 12, 2015) Dar Jennings said:
I have a whirlpool tub that I can't seem to get enough hot water to even cover the jets!

Plenty of hot water everywhere else.

Wondering if there is a scalding valve involved and where it would be located? We have a new hot water heater and plumber said I should be able to fill tub at least two times without running out of hot water!?

Reply:

Dar

I agree that there's a troubling problem, but it's not an anti-scald valve. Those valves mix cold in with hot to avoid scalding. They don't limit the volume of water that can enter a tub.

I'd start by doing a simple measurement, very rough, of the tub's dimensions so as to calculate how many gallons you need to fill the tub. Sometimes whirlpool tub sizes can be misleading.

Question:

(Mar 29, 2015) kenny said:
I have a peerless tankless oil burner and getting no hot water. Put a new mixing valve on about 6 months ago and it's been fine till today so I took the insides out and ran it and still water is ice cold. It seems that it's not getting any hot water thru the valve as the pipe coming out of the boiler to the valve is super hot. Could it be a clogged flow regulator on the cold supply line or the coil?

Reply:

Kenny

I agree that it sounds like a blockage; feel the pipes and you can find where the pipe changes from hot to cold - that's the obstruction. Usually.

If the coil were totally blocked you'd get no water coming out of the coil ahead of the mixing valve.

Question: redundant anti scasld valves or mixing valves?

(Apr 24, 2015) Leslie said:
I live in a 35 unit building with a boiler that has a mixing valve. Yesterday the water was shut done for a plumbing repair and today the hot water is scalding and there was less cold water in the shower. Does the set temperature on the mixing valve change when the water is shut off?

(Apr 27, 2015) Bill C said:
I am considering asking my plumber to install two, redundant mixing valves to prevent against scalding. I would prefer to provision my hot water source so I could set my hot water heater to relatively safe 120 F, but want to protect against bacteria.

So, I will likely set the hot water heater temp to 140 F, and use a mixing valve. Since scalding can be a serious injury, it seems prudent to employ a redundant design.

I wonder if you see any reason that a whole-house manual mixing valve, followed by a whole-house automatic mixing valve, or, two whole-house automatic mixing valves inline would be ill-advised? I am also planning to include a thermometer inline after each valve to monitor temperature and operating status of each valve. Thoughts welcome.

Reply:

Bill

I'm not sure I can give a definitive "right" answer, as there are different features or advantages of a whole house anti-scald versus point of use anti-scald.

Anti-scald built into a point of use such as at bath and sink controls on some homes can deliver hotter water, in particular if there are long piping runs (and thus heat loss) between the water heating source and point of use.

But safest and most economical is a single anti-scald valve or mixing valve at the water heater.

I might want both a whole house anti-scald valve and a point of use anti-scald valve if at a particular bath or fixture I wanted a second, lower delivery temperature: for example at the tub where the babysitter washes the baby.

(Apr 28, 2015) Anonymous said:
DanJoe, Thanks for your comments. I want same temp at all fixtures, just looking for extra protection in case of failure of one whole house mixing valve. Seems easier to install second whole house rather than retrofit a bunch of fixtures. Seems from your comments that redundant whole house is not common, but should not cause a problem with pressure. Does that sound like a fair summary?

Reply:

Bill: redundant mixing valves are indeed not common. A lot has been written about scalding hazards, particularly for children and the elderly. In performing scholarly research I could not find any references to duplexing anti-scald valves. If a valve fails to mix cold in with outgoing hot you will notice that immediately.

If you truly need the same temperature or precise temperature control at every fixture you'd need point of use anti-scald devices. That's because differences in supply piping length, location, routing, can make some differences in the temperature of heated water when it reaches the fixture. A single point of heating anti scald device sets the maximum temperature that may be supplied to fixtures. The actual temperature at individual fixtures will normally be a bit lower, lower still at the end of the longest runs. Insulating hot water piping reduces the en-route heat loss and can minimize these differences.

(Apr 28, 2015) Bill C said:
Thanks again. I just want a precise max temp at the heater, my pipes are such that that will give me consistent enough temp at each fixture. Just considering redundancy for added protection, to avoid someone discovering it right away at a bad timw and resulting in a scald. Seems like a prudent measure that should be more common in my opinion, even with the extra expense. But I guess many people have no scald protection, so whose to say.

...

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• ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES - home
• WATER HEATER TEMPERATURE TOO COLD or TOO HOT

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