Back pressure in hot line from anti-scald mixing valves?

[CLE]

Would appreciate any education on this topic. Went to replace a dead tank water heater in our church. Easy to isolate on the cold side. Seeing some back pressure from downstream on the hot side.

Water heater supports a church kitchen and is set at 140 but since it also supports a number of hand sinks, each hand sink has an aftermarket anti-scald mixing valve, thermostatic type.

I am assuming that when there is no hot flow, then cold can backflow from the cold line through the mixing valve and backwards through the hot supply line to the water heater.

Is this normal behavior for an anti-scald mixing valve or does it mean one of more our ours are defective?

Thanks,
Chuck in Virginia

 

[Nebojsa]

I could be wrong, but why so many anti-scalding valves. I think only one anti-scalding mixing valve right above the hot water tank should be sufficient.

 

[Sponsor]

 

[CLE]

To be clear, the hand sinks are piped along and then after the run to the commercial dishwasher and three-compartment dish sink. Output is 140 degrees so we were required to have in-line anti-scald at each hand sink to get tepid under 110. My question was about the function of such anti-scald valves. I know if the cold is shut off, the valve will shut off the hot -- it is the inverse I am wondering about.

If the hot is offline could the hot line be filling from the cold line retrograde back to the offline water heater, and is this normal behavior for these aftermarket add-ons?

I don't have the brand info for ours but think this is it:

https://www.watts.com/resources/references-tools/thermostatic-mixing-valves

 

[Sylvan]

"Water heater supports a church kitchen and is set at 140 "

Actually, 140 is the minimum a water heater should be set at to kill any bacteria BUT for the commercial dishwasher the minimum temperature should be 160 deg - 180 for sterilization in lieu of chemicals and usually, a temperature booster is required

Regarding the CW entering the HW, the line is common and a decent plumber would install a valve on the CW and HW of a heater so the tank like a boiler can be easily isolated without having to drain down the system.

It takes a certain mindset to try to save less than $40 and not install another valve

 

[Sylvan]

I could be wrong, but why so many anti-scalding valves. I think only one anti-scalding mixing valve right above the hot water tank should be sufficient.

Public restroom sinks should not dispense water hotter than 110°, and hand sinks for employees cannot exceed 120° by most state laws.

Therefore one temperature does not fit all applications so a Anti-scald device should be required

Where the elderly and toddles use a sink the suggested HW temperature is 100 - 105 deg MAX

 

[Sylvan]

I could be wrong, but why so many anti-scalding valves. I think only one anti-scalding mixing valve right above the hot water tank should be sufficient.

A commercial dishwasher requires 160 -180 for sterilization in lieu of chemicals

Water heaters should be a min of 140 to kill bacteria

Sinks for children or the elderly are required to have the HW set between 100- 105 deg

For the general public, the water should be no higher than 125 deg



https://www.hgexperts.com/expert-witness-articles/what-temperature-should-hot-water-be-6642

 

[CLE]

Right the dishwasher has its own built in booster to take to 180. The anti scald add ons at each hand sink takes them to around 110 max.

It was the backflow through these add on valves that is a pain.

As posted above, if valves had been installed on both water in and out of the tank I could have isolated the tank.

When I am done there will be valves on both!

 

[Sylvan]

Right the dishwasher has its own built in booster to take to 180. The anti scald add ons at each hand sink takes them to around 110 max.

It was the backflow through these add on valves that is a pain.

As posted above, if valves had been installed on both water in and out of the tank I could have isolated the tank.

When I am done there will be valves on both!

BRAVO

It is a crying shame when someone says they are a "plumber" and has no consideration for the next person that follows

Installing two valves ( 3 if there is a return circulation) shows professionalism and it is not like they are doing it for free this is part of the price for the installation

The extra valves allow the change out simple and save a lot of time

I am glad to see the dishwasher installer knew enough to install a booster and did not think 140 would be adequate

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