Triple Tube Smart40 Indirect Hot Water Heater

DH123

I installed a Smart40 18 years ago it worked great about a month ago it started leaking. So I was looking at my paper work and realized it was guaranteed for life if you had original bill of sale and register the H20 heater. The next day they told me I was covered so I found a plumbing supply store that carried Smart40 and started what I thought would be another great experience.

Since the original Smart40 started leaking I changed my circulator system from circulators on the return to pumping away. The only other thing that has changed is the separation between the supply and return pipes.

What I’m experiencing is the system will call for heat initially and doesn’t call again. I have changed the aqua-stat 2 times. It’s not the aqua-stat I can measure the resistance and it test fine at room temperature. The weird thing is when I pull the aqua-stat out of the dry well it is warm/hot to the touch. I’m thinking I’m getting some gravity feed that is elevating the temperature (resistance) of the aqua-stat enough so that it’s not calling for heat. I really don’t understand this because the water out of the H20 heater is stone cold after 2 minutes tops.

The tech support line is basically useless so I’m hoping someone here can help.

My gut feeling is that I reduced the separation between the feed and return lines that’s basically the only change between this Smart40 and the old one. I’ve been cruising the internet trying to find a definite distance requirement between feed and return piping and have seen one contractor say 18” to eliminate back flow.

Tomorrow I’m changing it to 23” the maximum I can get.

thoughts???

Jim Urquhart

Jamie Hall

Let's correct one thing -- an aquastat is a switch, not a resistance device. It may have only one set of contacts, or it may have several, and they will be, depending the particular type of aquastat, either open below a certain temperature, or open above a certain temperature.

It would appear the if you tested it at room temperature, and it tested "fine", which I'm going to assume meant you had conductivity, that the set of contacts which you measured close below a certain temperature -- which suggests that the set you tested was a high limit.

Now to determine what is needed in terms of piping, we really need to know more about how this thing is piped. This unit is an indirect, and should have four piping connections -- two from the boiler and two for the domestic hot water. I am not sure by what you mean by "separation between the feed and return lines" -- there shouldn't be any connection at all, although there might be if your heating is piped primary/secondary and there are individual circulators.

Please clarify -- pictures help a lot, and a good sketch also helps.

pedmec

post pics please

DH123

A couple things I didn’t mention. If I bypass the aqua-stat and just short the control
wires it works perfectly. Here is a picture of the new Smart40. Yes the ball valves are shut off it just produces cold water. I have an old electric H20 that we are using until I can get this thing figured out. You’ll see in the picture the supply line and the return line are at the same elevation. Is this a problem? This is the only charge in the set up.

neilc

if you're shorting the wires at the top of the tank,
and it works,
then it seems that control is bad,

but you're saying aquastat, is there another device there we don't see?
if so lift its cover and post a picture of its inside connections

Zman

What model boiler do you have? I am wondering if you old tank had sensor and the new tank is using a switch.

DH123

The wires are connected to the aqua-stat. I shorted them back to my Taco 506
the LED light comes on and all is good. So I’ve just proved it works fine once the aqua-stat calls for heat. The problem is the aqua-stat is hot ( high resistance) so it won’t call for heat, but I have cold domestic water in the H20 heater.


The 2 additional pictures show the Taco SR506 and the aqua-stat opened up so I could test.
You can see the gray wire attached to the aqua-stat it goes down about 30” into the dry well and comes out pretty warm even when I have about 1 minute of warm/hot water. If the temperature doesn’t go down the resistance won’t either and the thing won’t call for heat.

DH123

I have a peerless cast iron oil fired boiler.

DH123

The old tank was hitched up to the the same 506 Taco Control.

DH123

Again the only the different between the old tank and the new is a new circulator pump pumping toward the H20 heater and the distance between the return and feed lines. Previously the supply was on Black Iron above the boiler and the return was about 20” off the floor. A difference of about 4’. I have the supply and return manifolds at the same height. Is this a problem?

Jamie Hall

Does the aquastat ever call for heat -- that is, do its contacts ever close? Remember, it's a switch, not a resistor.

DH123

If Turn it up to scald it will come on for a little while then shut off.
If I try the domestic water I’ll have really hot water for about a minute then it gets cold. But the aqua-stat never changes resistance and calls for heat. In fact if I pull it out like I’ve said it’s very warm or hot to the touch ( high resistance). Weird. It almost like it’s not placed in a location that provides an accurate sample of the temperature in the H20 heater.

pedmec

its a switch, not a sensor as @Jamie Hall has said. It's an on/off device

kcopp

When you piped in the new tank did you put the dip tube into the cold side? if not you are short cycling the cold water and it heads right back out the hot side...

DH123

Hi Kcopp
The supplier asked me this on Friday and I was pretty sure I had put the tube in but after a quick shower of cold I positively determined it is in as called for.
I took a picture of it just in case.

kcopp

that needs to be installed on the cold side...
They give you a shorter one that is used for a recirc line.
The longer one goes in the cold.

DH123

Yes that is installed on the cold side. I took it out to verify and reinstalled it after the picture.

DH123

So having my supply and return manifold at the same height for 60” or so really isn’t an issue. This is the only difference between the old Smart40 and the new Smart40. My old system there was about a 44” separation. The best I could do if I lower my return is about 23”. Weird thing is I pulled the old aqua-stat out of the old Smart40 and it does the same thing. I don’t understand it.

neilc

let's try again,
if you run the hot water at the shower,
at the tank, do you feel the hot coming from the tank do the same hot, then cold, hot, cold thing ?

is it possible there's another fixture in the house cross connected?
a hose end shower head where the mix valve stays preset on, and you're regulating on a different flow valve,
or the kitchen sink?
outdoor shower ?

hot_rod

The aquastat probe needs to go down into the tank below mid point to read accurately

with hot water running in the house, the cold feed us cold and the hot line coming out us hot?

You could warm and cool that aquastat bulb with ice and a warm rag to see if it is accurate  

DH123

NeilC
I timed the amount of hot water I get about 30 seconds. The cold feels cold coming in and the hot feels warm leaving. About what I get at the facet.
Jim

DH123

Bob,
The aqua-stat goes down 30” I can hear it bottom out. I pull it up about a 1/4”.
If I was to cool the aqua-stat with ice or a wrap it’s resistance changes and it closes the loop
Allowing current to flow and the zone is happy. This occurs if I let it sit a room temperature for a while also.
Jim

DH123

I was thinking about getting a thermometer probe that you use for like a barbecue and feeding that down the dry well but I don’t have a cross reference temperature to resistance.
I’m not sure what I would do with the information.

hot_rod

There is no resistance involved with this control, it snaps on, snaps off. Much like the light switch on your wall. How are you seeing or measuring resistance? If somehow you are seeing resistance that control is not correct, the contacts inside are not closing properly.

If it is a cap tube type, The tube that goes into the tank changes pressure on a disc that activates the open or close switch. Really no way to measure that force, that I know of.

You could get any setpoint control with a sensor that fits in the well, Ranco 350 for example.

What type of boiler do you have? Many of the new boilers have the control onboard to run the indirect. Slip the boiler supplied sensor into the well, wire to the boiler board. Discard that aquastat.

Is there a sensor well between the boiler connections, near the bottom of the tank? If so slip the aquastat sensor into it and try it. It needs to fit tightly, most times you need to put transfer grease on the sensors to get good reading and accuracy.

You could also slip the sensor under the tank foam insulation near that hole in the jacket and try it. The sensor needs to be against the metal tank.

DH123

When I say measure the resistance that is exactly what I’m doing. The wire leads that Come off the aqua-stat and connect to my Taco 506. I’m measuring the internal resistance of the aqua-stat terminal for it to call for heat it needs to be a low or no resistance. As the temperature increases so does the internal resistance of the device. When I pull it out of the well it’s hot to the touch and measuring wide open. No current flow. It would seem like just change the aqua-stat but this would be the 3rd one in a week.
The boiler is a Peerless cast Iron oil burner. It ran the original Smart40 fine for 18 years.

DH123

These to pictures show me removing the leads going to the Taco506 and measuring the internal resistance of the aqua-stat. It order for this device to act like a switch the internal resistance needs to change. The first picture the potentiometer is set in the middle and it’s a high resistance the switch is open. the second picture it’s set would open and yes the resistance changes and it opens up like a switch. Even running the tank in this manner only produces a small amount of hot water.
It doesn’t make sense.

Jamie Hall

If you are reading ANYTHING except 0 resistance (well not more than 0.1 ohm) -- closed circuit -- or infinite (well, at least 5 to 10 megohms) on that "aquastat" you have the wrong device. Period.

DH123

I’m measuring.8 ohms and wide open.
I believe it’s a T100 that’s what it came with and what Webb’s gave me for a replacement.

neilc

in these last pictures with the meter,
is the white wire the probe ?

is the temp probe reaching all 30 inches down into its well tube?
it looks coiled up in this and the first pictures

neilc

well depth , 29 inches

pedmec

What is wide open?

pedmec

What do you mean by wide open? That's not a term related to troubleshooting controls. you know why yuo can't find a resistance value? Because its not what we call a k-type control. its a switch. if its a k-type sensor it would have a value, example a 10k thermistor reads 10,000 ohms at 76 degrees. a 5k thermistor will read 5,000 ohms at 76 degrees and so on. so your example of of .8 ohms means the switch is "closed". if it was "open" it would read "OL". Your resistance value changes are due to the temperature of the sensor, either "NTC" or "PTC". so put to bed that resistance valve. its less than one ohm and means nothing other than the switch is closed.

Jamie Hall

DH123 said:

When I say measure the resistance that is exactly what I’m doing. The wire leads that Come off the aqua-stat and connect to my Taco 506. I’m measuring the internal resistance of the aqua-stat terminal for it to call for heat it needs to be a low or no resistance. As the temperature increases so does the internal resistance of the device. When I pull it out of the well it’s hot to the touch and measuring wide open. No current flow. It would seem like just change the aqua-stat but this would be the 3rd one in a week.
The boiler is a Peerless cast Iron oil burner. It ran the original Smart40 fine for 18 years.

Several of us are trying to tell you that that is not how an aquastat controlling a burner works. Please. Read what we are saying.

Now this may not be the only problem -- it may be that there is some other problem, such as a wiring error, which is keeping the burner from firing. But I will say this: if the aquastat is reading close to zero resistance, and it is correctly hooked up to the boiler, the boiler should fire.

DH123

Hi NeilC
There are about 3-4 wraps of the gray wire as it comes out of the dry well and connects to the terminals. I have had sure that in bottom’s out in the dry well about 30” deep.

DH123

Thank you pedmec.
I’m just trying to get a brand new in-direct to produce hot water work and it’s making no sense to me. If you can think of anything I can try please let me know.

neilc

let's see how the wires are landed in the Taco
more pictures

DH123

The H20 heater is zone 6.

neilc

not sure why I asked for this,
we already know the wire and taco are good from you shorting the wire earlier,
gotta be that control at the tank

DH123

Ya everything points to the aqua-stat switch staying closed. Hard to believe 3 aqua-stat switches are bad.

neilc

DH123 said:

Hi NeilC
There are about 3-4 wraps of the gray wire as it comes out of the dry well and connects to the terminals. I have had sure that in bottom’s out in the dry well about 30” deep.

this doesn't sound correct,
that bulb sensor shouldn't be a wired device,
it should be a bulb, at the end of a thin tubing, connecting into the dial control,
it should not be gray wire landing on terminals,

DH123

That’s it.
I pulled it out for the picture.
Probably about 45” in length.
After it cooled for a minute have a look at zone 6.
Could it be this just isn’t closing long enough?




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