Aquastat L4008A help

John_Chapp13

I am a little confused on how my Aquastat works, this model 4008 seems to just have one temp setting plus a variable differential. Does this then function just as a low? All comments on here seem to refer to models with a Lo and High setting. It was set to 160 - recommended by one plumber - with 5 Diff on the wheel, but I am not getting all that much hot water in my shower now. Additional Aquastat on the indirect water heater set to 120 - recommended by a different plumber to save oil which it seemed to do and hot water was fine. 3 story, 1600 sq ft, steam radiator house in NY. Oversized, old oil boiler from when the house was not insulated. Goal: I am trying to minimize oil use, after spending $100/m in the summer just to heat 45g hot water tank. Any recommendation on settings and how that Aquastat works? Pics attached. Thanks!!

John_Chapp13

Photos attached here.

EdTheHeaterMan

The L4008 series of controls are single pole single throw or single pole double throw switching action thermostats. This means that the R and the W will make on temperature rise and the B and the W will break on temperature rise.

The differential is an adjustment of the difference between the switching action from temp rise to temp fall. If the temperature is set at 160 and the differential is set at 10 then the R and W will open or "Break contact" when the water temperature reaches 160°. As the temperature cools the R and W contacts will not connect or "Make contact" until the water temperature reaches 150°, which is 10° colder than the set point.

If you change the differential to 20 then the water temperature must go to 140° before the switching action changes back Make contact on R and W, which is 20° different than the 160° setting.

I could not open your pictures to see what you have. I believe those are file designations on your computer, not internet accessible.

there is a picture icon above that may be able to post your .img files

STEVEusaPA

You can attach the photos to you post directly.

John_Chapp13

Can't get the photos to upload properly but he's a Flickr album with them: https://flic.kr/s/aHsmS6YVK9

EdTheHeaterMan

OK saw the L4008A control That has only the R and the W. So there is only a break on temperature-rise set of contacts.

It is your only high-temperature limit switch on the system. It is also an operator control. Good for residential but would not be enough for a commercial installation. The operator control can not double for a "Safety" limit control on a commercial job.

To answer your hot water query... set the L4008A to a minimum setting of 180°. you may need 190° or 200° but start low at 180°. The higher you set the control the more fuel you will use, but there is the other side where if it is too low you will not get enough heat for design conditions. That means the radiators won't have enough heat to reach the desired room temperature when it is really cold because the water in the radiators is not hot enough at 160°

This is obviously your condition right now with not enough hot water. The radiator inside your hot water tank is not getting hot enough to keep up with your need for hot water. If you picture your hot water tank like another room in your house it will be easier to understand.

The room radiators have 160° water n them to make the room temperature 70° The radiator in your water tank may need 180° to make the room 120°

I hope this helps

edit:

The differential can be set higher like 10 or 15 in order to stop short cycling (or make the off-time longer) because short cycling wastes fuel.

John_Chapp13

So set at 180 and change Diff wheel to 20 would mean we shut off once 180 is reached and go back on at 160 right? Is that a recommended setting for a smaller house? Not sure why it’s set to 5 Diff. And any thoughts on weather tank temp vs boiler temp settings?

EdTheHeaterMan

Yes

EdTheHeaterMan

The tank temperature should be set at 110° to prevent scalding. But many people set them higher. But I would not go higher than 125° unless there's a mixing valve on the hot out pipe. That is where my ex-girlfriend likes it. But it is too hot for me

EdTheHeaterMan

John, a closer look shows that you have a mixing valve. your insufficient hot water may be at the mixing valve. They can fail from time to time.

The water in the tank may be hot enough but the mixing valve will have a hot-in and cold-in. Then there is a MIX out with the water temperature you get at the tap. The out water from the tank enters the hot-in to the mixing valve. the thermostat in the mixing valve determines if the water temperature is too hot for the setpoint and adds cold water to it, so you get the desired temperature. You may have a mixing valve where the setpoint is set too low, or you may have a bad thermostat in the valve, or you may have debris stuck in the cold-in portion of the valve letting too much cold into the Mix-out port I would check there first.

ethicalpaul

I can totally sympathize with your desire to separate your DHW from your boiler. Why anyone ever decided to combine those together is beyond me. Maybe there was an OK reason at one point in the past but that point is far far in the past.

Cut that thing out with extreme prejudice and replace it with something like https://www.homedepot.com/p/Rheem-Performance-Platinum-50-Gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE50T10H45U0/312742081

You can get cash incentives to take down the cost, and the annual operating cost is so very very tiny.

EdTheHeaterMan

@ethicalpaul Paul has a good idea for when you are ready to make that change. The mixing valve test and aquastat settings are to get you back to normal now.

OFF TOPIC>
Paul, are these water heaters that use heat pump technology to reduce the cost to heat water electrically? Have you used them? What happens to the cold side (evaporator coil)? Is it contributing to cooling in summer and adding to heat load in the winter?

John_Chapp13

@ethicalpaul So I have a direct water heater? I was told it was direct at one point but was converted over to indirect, is that not true? Sorry I know just about nothing here, have lived in NYC apartments for most of my life. Also is the 180 high, 20 Diff sound about right? 

I actually looked at those heat pump water heaters but was told by another plumber that I would regret it come winter and 3 people showering...

John_Chapp13

Someone on Reddit said my boiler water level is too low and it should be half in the glass tube, does that sound right?

SuperTech

Heat pump water heaters are great for reducing electrical consumption, but they don't recover as fast after heavy usage such as long hot showers. But anything is better than a tankless coil. @John_Chapp13 it seems like you have the correct understanding of how the aquastat settings work, I would use a 180 high limit with a 20 degree differential, maybe even 25 degrees. Short cycling is the enemy of all heating and cooling systems. 

EdTheHeaterMan

After looking closer at your pictures, I have a thought about your original query "Not enough HW". Does the problem go away when the boiler is fired for space heating? During space heating the water temperature goes to over 210°F to make steam... that overrides the L4008A setting.

if your problem goes away during a heating cycle, then the aquastat is set too low. If the problem does not go away then you may have a mixing valve problem.

Since you indicated the issue started after the plumber set the L4008A to 160°, I would bet the problem is that setting

John_Chapp13

I haven't used heat for the house yet since the change but will test that out. Thanks!