I converted the tankless coil HW in my old (1975) American Standard oil fired boiler to a variation on indirect HW (with help from a friend who used do plumbing for a living). Reason was the coil wasn't producing HW rapidly enough, probably due to scale reducing heat transfer. I was going to put a new one in and was advised that some of the bolts were pretty rusted and it has happened that the boiler is damaged when trying to remove the old coil. The solution, although more expensive, was to add an insulated HW tank w/ a thermostatically controlled circulator that runs through the tankless coil. So I basically have a 40 gallon HW 'capacitor' which gives me enough HW.

The set up has worked great for about 10 years but this morning I was running out of hot water. A hand on the coil output to tank was luke warm but is usually too hot to hold on for long. So it appears no circulation. Ass uming the tankless coil hasn't plugged, it can only be a problem with circulator or aquastat. Would my first step in trouble shooting be to bypass the aquastat and see if I get circulation?

 

The tankless isn't plumbed correctly. It should not be using the coil in the boiler for heat, it should be using the boilers primary water to heat the tankless.

I think you should have that corrected, you'll save much more in fuel too.

 

Tom, he doesn't have an indirect heater, just a storage tank connected to the tankless coil.

Mike, can you post a few pictures of the piping setup? It could be the circulator is not running or it could be an air trap preventing the water from circulating. Ascertain the pump is working is the first step.

 

Tom, it sounds to me as if he's describing an 'aqua booster' (google the term for more info) setup which is a perfectly legitimate setup... still not ideal of course, it still uses the tankless coil and the boiler is still warm started, but not 'wrong'.

I guess that's one way...

 

Troop, Furd - I reread that post again, didn't catch the HW Tank part. I should finish my coffee before I respond. Thanks for pointing that out!

 

It was working when I got home tonight so I may be dealing with an intermittent problem. At least I know it can't be a plugged coil. I listened to the circulator with a screwdriver (Taco 006, it's very quiet) and heard no worrisome noises. I have a jumper wire ready for the thermostat if it happens again... Here's a picture of the hookup diagram and the installation.

 

Mike, what happened to your plant? I think that was you, wasn't it? I thought maybe you were doing some indoor 'farming'...

I know you know that a'stat circuit is 120 VAC and that you won't hurt yourself, right?

 

Ha ha! Yea it was my plant... You have a good memory! Thanks for the head's up on the voltage. That was the first thing I checked with my DVM. On the subject of that T-stat, there's a Honeywell logo on the case but the only part number I can find is on a sticker inside the cover. I searched around and couldn't find any reference to it (95-3534). I'm not sure exactly what is called either. Is it a theremostat, aquastat, immersion aquastat, thermostat relay? I did some reading on the Taco 006 and it shows a small circuit board under the power input cover.

 

What was on the sticker besides the 95 number? or was that it?

It's probably an aquastat, maybe a 4000 series... can you pop the cover and take a pic?

 

A few pics of the t-stat.

 

I think if you look closely you will find a number on it... L4080 something or other... like in the example photo:

 

Thanks NJT, I'll have to break out the magnifying glass and a better light!

 

I'm reading L4080B 1360 in the photo, "upside down" from the boiler plate (decal/sticker); but right side up in the photo.

 

I'm not sure what you're saying.

Did you find the number on your control? and it's the same as in the photo?

 

I think Vermont was reading the number on your example photo NJ.

 

Ohhhh... I didn't even notice it was VT that posted that!

I thought it was YOU!

Did you ever find the number on yours?

 

I did finally get out a magnifier and flashlight and found the number. L4040B1295 high limit aquasat. The old one checked out O.K. with an ohm meter after disconnected but I replaced it anyway... I have a feeling it wasn't the problem.

The circulator seems to be doing its thing based on I can hear a difference between when it's running and when I shut it off (using a screwdriver as listening rod since it's very quiet). I do notice the tankless coil to water tank pipe is not hot to the touch as I remember it to usually be. I also notice the pipe temperature is very stratified (hot for the first 1 - 2 foot leg out of coil, then gets cooler as pipe goes up to top of tank) while the water at the tap is warm but definitely not as hot as it should be.

Is there a way to test a circulator?

 

M,
Probably the simplest way is to turn up the aquastat on the tank which should start the pump and then turn on the boiler which would deliver hot water to the tank. If you think it may be aquastat you can jump it to see if the pump starts. Take a pair of needle nose pliers with rubber grips and touch the 2 screws. Nothing will short out, it's a series circuit. There's no common there.
If you have a meter and know how to use it you can activate the aquastat and see if you get 120v at the pump.
If you do and nothing happens that's most likely your problem.

 

Show me a picture of the top of the tank and the pump. Although unlikely it is possible that an air bubble has formed at the pump suction and is preventing circulation. Or, you may have lost a pump coupling if a three-piece pump or maybe even had the impeller come loose from the motor shaft with a "canned" pump.

 

I've attached a photo showing the top of the tank and pump. It's a bronze Taco 006-BT4 (cartridge type). I'm curious if anyone has an idea how quickly to expect the aquastat response to how water demand? I noticed last night when hot water was being used for a shower, the pipe from coil to tank was barely warm even though circulator was on. I also happened to notice the cold water supply pipe is really cold (not sure how deep the water pipe to house is buried). Could colder than normal supply water be partly to blame for slow response? I did check the coil to tank pipe again about 1/2 hour later and it was too hot to touch for more than a second.

 

Sure it would!

And had the tank recovered?

 

The way that pump is mounted is susceptible to air trapping in the suction piping. It really should have a 90[SUP]o[/SUP] elbow at the tank, the pump horizontal (with the motor also horizontal) and then the suction piping cut down to turn directly to the pump.

 

There is hot water at the tap... Seems like it takes longer to get there but that may be my imagination...

I was looking at indirect heaters and wanted to be sure I have the basics.. The main component is an insulated hot water tank with a heat exchanger coil inside. The coil can be plumbed as a separate zone from the existing boiler. Does that mean it would be just like adding a zone to your heating system with a thermostat controlling zone valve and circ? The boiler uses a Honeywell R8182D which (I think) is a triple aquastat although I'm not really sure what that means....

 

I just saw your post Furd. I think I understand what you are saying. The pump impeller housing should be rotated 90 degrees so suction and pressure side are horizontal rather than vertical as it is now. But would air trapping not have been an issue from the start? The intermittent hot water is something only happening recently.

 

I'm not saying the present mounting IS a problem, just a potential problem that can be easily rectified.

 

PARTICULARLY with pumps that have IFC (internal flow check) in them, that are pumping into the vertical, air can collect behind the flow check and prevent it from pumping.