Tankless Coil Aquastat Settings?

Kafox15

I have a Peerless WBV-03 single pipe steam boiler with a tankless coil and I just want to make sure the aquastat for the DHW is set appropriately. Its a Honeywell L4006 that only has Hi and Diff adjustments. Does that mean Lo is automatically Hi minus Diff? Currently, Hi is 180 and Diff is 10, but my research shows Diff should be more like 20, but wanted to double check.

EDIT: Changed L6006 to L4006

Big Ed_4

Depends if your good with the output of your hot water during the down cycle of calling for heat . Set at 180* with a 20 diff will turn on at 170* and shut off at 190*

Kafox15

Big Ed_4 said:

Depends if your good with the output of your hot water during the down cycle of calling for heat . Set at 180* with a 20 diff will turn on at 170* and shut off at 190*

We never have an issue with running out of hot water, though we do notice lower hot water pressure from time to time - which could just be the tankless coil showing some age.

Is 180 setpoint with 20 Diff a typical default setting? I am still not clear on how the diff works.

EDIT: Oops, I had the wrong model number before. Its actually an L4006A with setpoint and diff. Does this change anything?

Kafox15

Following up. Can anyone answer my last questions? Thanks

EdTheHeaterMan

The adjustable differential is there to reduce short-cycling of the burner. I believe it adds to the temperature setpoint That means if you select the minimum differential of 10°F and you set the control at 180°F the burner will maintain a temperature between 170° and 180°. When the water temperature drops below 170° the switch contacts make and the burner operates. Once the water temperature reaches 180° the contacts open and the burner stops.

When you adjust the differential to 20° the new high limit is 190°. 10° more than the setpoint of 180°. The contacts close when the temperature drops below 170° and the contacts open when the water temperature rises above 190°. It is just a switch that turns on and off based on the temperature you select and the differential; you select.

Regarding the water pressure, you should have a mixing valve on the system. That mixing valve may be partially restricted. A good cleaning of the mixing valve and the tankless coil will bring the system back to optimum performance.

EdTheHeaterMan

Further investigation reveals the differential is a "Midscale Differential". What this most likely means is that a setting of 180° and a differential of 5° would cause the actual high limit to be 182.5° and the cut in temperature is 177.5° to be determined by actual testing after installation.

If the differential is set at 10° then the 180° setting was actually 175° cut in and 185° cut off.

Set the differential at the maximum of 30° and the 180° setpoint and the high cut-off would be 195° and the low cut-in temperature would be 165°. This would also need to be verified by actual testing after installing the control.

The actual reading on the thermostats, controls, and thermometers have liberal tolerance. Testing is the fail-safe of the installing technician. Just installing the part without verification is not good practice.

Kafox15

Thanks. That is all very helpful. What are some good default settings I should start with and then tweak based on the results?

EdTheHeaterMan

I would start at 160° setpoint and 10° diff and see if you have enough hot water. If so your off-cycle loss will be less at 160° than at 180° setpoint. The lower the minimum temperature the less fuel you will use. But don't give up comfort for a few dollars in savings.

bburd

Since it’s usual for incoming cold water to be colder in the winter and warmer in the summer, you may find that you can use a lower aquastat setting in the warmer months.

Kafox15

Have my setpoint at 160 with a diff of 10 and water temp is perfect coming through my mixing valve. I also took apart the mixing valve and cleaned it out though there was not much build up. What's the best way to flush my coil? I've read about pumping in a vinegar mix but any other options?

Somewhat related question - the water pressure entering our house is ~80 psi which I understand to be a bit high but not crazy. Is it worth installing a pressure reducing valve at this pressure? And if I do, do I need an expansion tank for my coil?

EdTheHeaterMan

To make a short answer LOOOOOONG
A pressure reducing valve PRV set at say 50 PSI would be a good idea for all the valves and fixtures on the system. less stress on the moving parts... "Yada... Yada... Yada..."
If you have a PRV you should install a small expansion tank for the same reasons as the PRV (all those Yadas above). As the cold water from underground piping enters the home and warms up to room temperature, it will expand and increase pressure if there is no place to go. You see the PRV acts like a check valve and will not allow the expanding water to flow back into the water company piping system (backward thru the meter.) Your water meter may also have a backflow preventer connected for that same reason.

Also, the water in the tankless coil will expand once the hot water valve, tap, or washing machine solenoid valve closes. Since there is no "top of the water heater air cushion" to accept this expansion, and in many cases, there are no relief valves on tankless coils (I could never figure out why that was not enforced) the pressure exerted on many faucets and valves can be tremendous. But it goes away as soon as someone opens a valve (like the ice maker on your refrigerator).

Regarding the tankless coil cleaning, There are 3 that I have used successfully. All three require that you have isolation valves on the hot and cold water side of the coil and a boiler drain valve on either side of the coil between the iso valves and the coil. This way you can flush the mess out of the pipe without putting any of the debris into the rest of the hot water system throughout the house... clogging up all the little strainers.

After the valves are in place you can try the first one. It is free.

1 Shock the crap off
A. First, you need the get a garden hose about 3 to 5 ft long (Washing Machine connector works well)
B. You also need a 5-gallon pail.
C. Connect the hose to the boiler drain of the hot outlet of the coil.
D. Set all thermostats in the home to off or the lowest temperature. No calls for heat. and record where the aquastat settings are.
E. Set the boiler high limit to 235°
F. Set the low limit to 225° Turn on the switch to operate the burner.
G. Once the boiler temperature is at 225° let the water in the tankless coil absorbed the heat for a minute or so.
H. Place the free end of the garden hose in the 5-gallon pail. You may want to have something to clamp the end of the hose so it stays in the bucket.
I. Close the cold water inlet to the tankless coil and then open the boiler drain on the hot discharge. The water pressure in the coil will drop to atmospheric pressure and the water in the coil will flash to steam shocking off a significant amount of crud and crap.
J. within a few seconds, after the pressure is released, open the cold water supply to the coil and shock the coil again with cold water against the hot copper inside the boiler.
K. close the boiler drain to the 5-gallon pail after the water runs clear.
L. Empty the bucket and let the boiler heat the water in the coil for about 10 minutes.
M. Repeat steps H thru L for a total of 3 flushes.

2 Acid the crrap off
A. Shut off the hot and cold water valves to the coil
B. Open the boiler drains
C. Connect hoses to the boiler drain valves and place one in the 5-gallon pail.
D. Using a hand pump or standpipe apply 1 part Hercules Sizzleand 2 parts water into the coil until it runs out the other side drain valve.


E. Let it sit until foaming stops.
F. Add more sizzle as needed.
G. Adding more sizzle with no foaming means the coil is clean.
H. Flush the coil with cold water of all the chemicals and run water out the hot water drain for 5 minutes after the chemical has cleared.
I. Use the enclosed test to be sure the water is at the proper pH before opening the hot water isolation valve.
J. Flush all the hot water faucets for about 2-3 minute each, to be sure all the chemical is gone from the system before drinking, cooking or showering.
Caution this acid may cause the copper pipe to fail if the corrosion is extensive. You may need to replace the coil after procedure #1 or #2 ...but that would happen soon anyway without cleaning.

3 Maintain the crap off
Use vinegar-based cleaner or tankless coil cleaner on a regular basis (annually or bi-annually) depending on your water condition. Here is a good kit to use.

Do NOT use this setup with Hercules Sizzle.

https://www.homedepot.com/p/Flush-Kit-for-Tankless-Water-Heaters-RTG20124/202798886?source=shoppingads&locale=en-US&mtc=Shopping-VF-F_D26P-G-D26P-26_10_WATER_HEATERS-MULTI-NA-Feed-PLA-NA-NA-WATER_HEATERS&cm_mmc=Shopping-VF-F_D26P-G-D26P-26_10_WATER_HEATERS-MULTI-NA-Feed-PLA-NA-NA-WATER_HEATERS-71700000033150351-58700003868932468-92700049176334365&gclid=Cj0KCQiA0fr_BRDaARIsAABw4EsPV0QrLRg3tH2mAAVNnek6EmkJyLi7ijANsrQOy1AHT4Bi7RsOujIaAvjIEALw_wcB&gclsrc=aw.ds

Yours Truly,
Mr.Ed

STEVEusaPA

EdTheHeaterMan said:

To make a short answer LOOOOOONG...

Isn't that your specialty?

Kafox15

Wow - lots of information for me to digest. Thank you. I will note my boiler is steam so I don't quite have the temp control abilities mentioned in cleaning option 1.

Would I need an actual expansion tank or would a large water hammer arrestor like Watts 150A suffice? Also, where on the system would the expansion tank go? I know my mixing valve has check valves on both the hot and cold inlets.

Kafox15

Following up on my last post.

"Would I need an actual expansion tank or would a large water hammer arrestor like Watts 150A suffice? Also, where on the system would the expansion tank go? I know my mixing valve has check valves on both the hot and cold inlets."


As far as cleaning, think I'll probably wait until summer when I won't need the boiler for heat since I'll need to add valves to connect the hoses to the coil etc.

Kafox15

Wanted to follow up here again @EdTheHeaterMan

EdTheHeaterMan

You have a steam system. So there is no expansion tank... and... you can do step #1. Keep in mind that the water pressure in the coil is separate from the steam pressure in the boiler. There is a wall between the two waters The steaming water is in the boiler but on the outside of the tankless coil. The potable water is on the inside of the tankless coil so it is still under pressure and will not boil when the boiler is steaming. Once you open the purge valve to let the water pressure out, the shock will happen and break off the deposited inside the coil. I will need to rewrite the instructions for steam boilers (the instructions given are for hot water boilers)

That is what happens when you just copy and paste without reading the information.

EdTheHeaterMan

Here is the revised instructions for a steam boiler.

A. First, you need the get a garden hose about 3 to 5 ft long (Washing Machine connector works well)
B. You also need a 5-gallon pail.
C. Connect the hose to the boiler drain of the hot outlet of the coil.
D. Set all thermostats in the home to off or the lowest temperature. No calls for heat. and record where the aquastat settings are.
E. Set the boiler high limit to 235°
F. Set the low limit to 225° Turn on the switch to operate the burner. and jump out the thermostat or turn it up to 90°
G. Once the boiler temperature is at 225° begins to make steam, let the water in the tankless coil absorbed the heat for a minute or so.
H. Place the free end of the garden hose in the 5-gallon pail. You may want to have something to clamp the end of the hose so it stays in the bucket.
I. Close the cold water inlet to the tankless coil and then open the boiler drain on the hot discharge. The water pressure in the coil will drop to atmospheric pressure and the water in the coil will flash to steam shocking off a significant amount of crud and crap.
J. within a few seconds, after the pressure is released, open the cold water supply to the coil and shock the coil again with cold water against the hot copper inside the boiler.
K. close the boiler drain to the 5-gallon pail after the water runs clear.
L. Empty the bucket and let the boiler heat the water in the coil for about 10 minutes.
M. Repeat steps H thru L for a total of 3 flushes.

Kafox15

Thanks for the updated instructions @EdTheHeaterMan. I obviously don't have high or low limits, so that's the part that didn't make sense to me.

Still looking for an answer to these questions if you don't mind. This is in reference to me adding a PRV on the system.

Would I need an actual expansion tank or would a large water hammer arrestor like Watts 150A suffice? Also, where on the system would the expansion tank go? I know my mixing valve has check valves on both the hot and cold inlets.

EdTheHeaterMan

No need for a pressure reducing valve on steam boilers. The PRV would be for the whole house potable water... so just after the meter is the best location. The location of expansion tanks is a question for the plumbers herein. I would say that you need it near the tankless coil, between the coil and a check valve that will not allow for the release of pressure because the water can not reverse past the check valve.

You also need to provide for expansion anywhere there is a valve that prevents the release of pressure in reverse to any other expansion allowance device, meaning you may need more than one if there are multiple check valves and backflow preventers. This is where you have to think like water in your mind's eye and say "If I were water where would I go if heated?" If there is no place then you need to make a place.

Kafox15

Yes, I understand where the PRV needs to go. I just don't know where the expansion tank needs to go. So if anyone else might be able to answer, it would be much appreciated.

EdTheHeaterMan

The more I think about it, the only logical place is after all the check valves. As water expands from heating, it needs a place to go. it will go thru the check valve to the next check valve and the next check valve to the expansion tank. Then as it cools it will shrink. Not such a big problem. It will never cause a vacuum because the city water pressure will fill the void. We want to stop extreme hydraulic pressure so the best place is on the mixing valve's Mix water out port to the faucets. The tank's air cushion will take up the pressure and compress as the water expands. As soon as a hot water tap is opened, then the tank will reset to the tank charged pressure. That should be set to the PRV pressure setting.

@hot_rod or @Youngplumber should be able to verify the potable water expansion tank location. I'm an oil heat and Hydronics guy.

Respectfully submitted,
Mr.Ed