Honeywell AM-1 DHW Mixing valves not working, big puzzle

Jells

I have 4 small apartments with a tank water heaters providing DHW and heat. The mixing valve in one seemed to crap out after some years, giving ~80 deg water. I replaced it with one I rebuilt with their kit. Same. Another rebuilt. SAME!!! Ordered a new one, 80-145 instead of 70-120. SAME!!!!!!!!

They always seem to work right after I install them. If I opened up all the taps and shower on the call from the tenant it seemed to get better. My only theory is I need an air exclusion vent over the valve, since that's an unvented loop, and if the flow isn't enough the air will stay there. It still doesn't really explain the valve, since the cold is flowing down into it. Or why all of a sudden, unless perhaps there's been a change in pressure I never noticed, but the unit on the same top floor has no problems. Talked to Honeywell. No ideas other than pressure and inlet temp. I'm out of ideas.

The valve is installed cold up, hot down, mixed heading out the back to the home.

STEVEusaPA

Inlet temperature is the killer. Your also right up against the flue pipe, although I don't think it's hot enough to cook it.
Is there anyway to verify the temperature right at the inlet. You're water heaters could be overshooting
But the real problem...the REAL problem is that you are doing something wrong and dangerous by using that water heater for both heat and domestic hot water.

Paul48

Can we get a better picture of the piping? You don't need to vent domestic water supply. Is that a circ on the cold feed? Ever watch a dog chasing it's tail? Not that I can be sure, but it appears the way you have it piped, the more cold the valve needs, the less hot that's available. The valve is more confused than we are, if that's possible.

STEVEusaPA

Paul48 said:

Can we get a better picture of the piping? You don't need to vent domestic water supply. Is that a circ on the cold feed? Ever watch a dog chasing it's tail? Not that I can be sure, but it appears the way you have it piped, the more cold the valve needs, the less hot that's available. The valve is more confused than we are, if that's possible.

Have another read, he said he's using it for heat and domestic hot water.

Jells said:

I have 4 small apartments with a tank water heaters providing DHW and heat.

Paul48

Wow.....I need to read better. Thanks for pointing that out @STEVEusaPA . The best advice, is, get the saw-zall out.

hot_rod

Could be a broken dip tube and it is not seeing hot water? Ideally the tank runs 25° warmer than the mix temperature.

Or could the radiant load be running an pulling down the temperature?

Jells

Thanks for all your thoughts. I've spent many hours on this, several on the phone with Sparco. They have no theories. Further data is that if I open up both sinks and the shower full hot, the valve will work properly. And the supply pressure in the tank is on the low side, 35 psi. Amazingly, utlity claims their supply can legally go as low as 20psi in the street, which would mean near zero at the 4th floor showerhead.

I added an air excluder valve to the vertical pipe on the cold water ( that leads to a sprinkler head), on the theory that air was getting trapped in that loop. No change. As a stopgap, kick the can down the road till I can resolve this, I've gutted the valve and blocked the cold feed so the DHW is getting it straight from the heater and turned down the tank to normal temps. 4th floor actually may never need more BTU's than that temp provides.

And sorry Steve, I'm not interested in debating a safe, and at least locally legal design that has tank heaters designed specifically for it's use and has served me mostly trouble free for 15 years in my oldest system.

EBEBRATT-Ed

If I am looking at this right the return from the heating loop is teed into the cold water line so you are bringing ( hot water or warm) into the cold water feeding the mixing valve. not sure what effect this will have on the DHW

Something you might try. Disconnect the heating line return pipe from the cold water line. Pipe the heating return into the water heater tank drain valve with a tee

hot_rod

Hard to see how the upside down pump connects to the mix valve. Typically you pump away from the mix valve so it pulls from H&C ports to mix properly.

Why does the system need a mix valve? What temperature does the tank run? What temperature is required for the hydronics?

Jells

Given the heating is not running (been warm here) the circulator is really not the issue. Not to mention it's been working this way fine for 7 years, and I have 3 more trouble free units. Just to clarify, the circulator is for baseboard heat, not always hot tap water. The heater is set to HI for max BTU's from the baseboard and lower Legionella risk, and the mixer is supposed to supply ~115 deg DHW.

EBEBRATT-Ed: regarding where the mixer would get cold water, that's an interesting question. Can we assume the pressure is additive, that the whole system is under line pressure, and the circulator adds PSI to that side of the tee? Either way, since the mixer has a limited temp difference range, it should actually work in it's favor having to mix water closer in temp. It would just take more from the cold than it would otherwise. But it seems getting too much cold could hardly be a symptom of too warm a cold supply.

I've seen that Taco makes a mixer with the same frame, I may get one and see if I still have the same problem. Odd that the ones I see are 85-176 (Taco 5002), and none in the 70-120 I've been using.

Jamie Hall

I'm with @STEVEusaPA 's initial comment on this one. I have no doubt that you have been doing it this way for many years. I have not doubt that you are perfectly happy with it. I also have no doubt that you aren't interested in spending the money to do the thing properly. OK. None of that makes it right or correct. It does, however, make it rather difficult to correct problems when they do arise.

Jells

Ok Jamie, since it seems I've stabilized my problem and no usable help has come of this thread, I'll bite. What exactly is wrong with using a water heater explicitly designed for minor room heating for that purpose, and what would you install in a 450' apartment with no option for direct vent appliances? I'm all ears. The biggest local heating distributor here creates "kits" of these with the heater, directions, and all the parts required.

What the professionals installed here 1st (before they installed this type subsequently in another unit) was a Minitherm boiler and a 30 gal indirect tank. It was noisy, high maintenance, and a huge footprint in a tiny apartment, 3x the space requirement of this system.

Oh, and this isn't academic, I have another of these apartments to reno. I'm open to better ideas, I just haven't seen one.

KC_Jones

http://www.contractormag.com/news/cm_newsarticle_266

Read up, it's not taken seriously in this country and that's why people install systems like you have.

hot_rod

Here is an option. This was my go to system for small area hydronics.

A basic tank type water heater with a coil inside to separate the radiant.

And a drawing on the best way to pipe a 3 way thermostatic.

Jells

KC_Jones, that's a reasonable argument I hadn't heard. I thought I was ahead of the game regarding Legionella keeping the tank at max temp. But tell me this, doesn't the same argument hold for all the water cooled off in any hot supply line then getting sprayed while you wait for it to get hot? And what about the fact that the return water is sent into a 140 deg hot tank? Would that not kill the legionella?

The suggestion " use a flat-plate heat exchanger and run the domestic hot water side as constant circulation." seems perfectly reasonable and doable, I guess the reason the DHW side circulator must run constantly rather than with the heat call is so there's never water cooled off in there. I hope the exchanger is insulated well so there's no big increase in passive losses.

Hot Rod: I've been using the B-W with side taps but without the coils, except in this unit where the closet was built for that minitherm and was too narrow for the B-W. I guess I should price out the difference in cost and hassle between the built in and external exchanger.

SeymourCates

Legionella dies in 30 minutes at 140F. Returning to the tank held at 140F or above can only offer risk if there is no waiting period in the tank for the return water. Such a situation could possibly occur during simultaneous DHW demand with CH demand.

With regard to the FPHX solution, continuous circulation can be achieved without the circulator simply by convective transfer.

The DHW loop to the FPHX can remain off for the entire season where heat is not required provided that care is taken when it is utilized for the first time in the heating season. It would be wise to run the loop at maximum temperature available from the WH for one hour.

Henry

That tank is not certified to be used as a heating source. If by bad chance someone gets ill, you will take complet responsabiity and all associated costs.

Jells

So, the valve saga continues, but now I'm closer to the culprit, and its not the valve. Tenant texts this morning there's no HW. ****? There's no cold feeding that valve now!! It's not even a valve anymore, its effectively an elbow!!

Turns out both check valves on the heating loop are failing and cold water was feeding back through. When I increased the flow by opening all 3 taps the check valves would close and there would be hot water. And every time I screwed with it and left, it was working because the screwing around loosened the checks, but apparently then hours later the checks froze again and no HW once more. These are swing not spring checks, and when I tried to open the service cap it was not happening. They have to go. A question is whether the spring type is better than gate for some reason.

There's still one more puzzle piece. Why was the water feeding back through at all? The CV of the loop should be enough to prioritize the flow from the straight shot down into the tank. Can there possibly be an obstruction in the few inches of pipe from the tank to the tee? There's no dip tube on the hot, right? It's just straight from the top of the tank. Can there be a heat trap valve in there failing and blocking flow?

Henry, are you saying the mfrs of these tanks that have side taps for heat loops, and directions in their manuals for using them for heating, are selling them for that purpose without certification?

Solid_Fuel_Man

How about Taco XPB to separate the DHW from the heating side. That would allow you to still use a water heater as both heat and DHW, but makes the heating closed loop.

You could also make your own with bronze circulator, and a FPHX with an iron circulator and an injection controller as the Taco uses a rebranded Tekmar.

Rich_49

Jells said:

So, the valve saga continues, but now I'm closer to the culprit, and its not the valve. Tenant texts this morning there's no HW. ****? There's no cold feeding that valve now!! It's not even a valve anymore, its effectively an elbow!!

Turns out both check valves on the heating loop are failing and cold water was feeding back through. When I increased the flow by opening all 3 taps the check valves would close and there would be hot water. And every time I screwed with it and left, it was working because the screwing around loosened the checks, but apparently then hours later the checks froze again and no HW once more. These are swing not spring checks, and when I tried to open the service cap it was not happening. They have to go. A question is whether the spring type is better than gate for some reason.

There's still one more puzzle piece. Why was the water feeding back through at all? The CV of the loop should be enough to prioritize the flow from the straight shot down into the tank. Can there possibly be an obstruction in the few inches of pipe from the tank to the tee? There's no dip tube on the hot, right? It's just straight from the top of the tank. Can there be a heat trap valve in there failing and blocking flow?

Henry, are you saying the mfrs of these tanks that have side taps for heat loops, and directions in their manuals for using them for heating, are selling them for that purpose without certification?

I think what is being missed here is the necessity in some codes for pump exercise at intervals so water is not sitting breeding Legionella . Some codes do not recognize this but it is effective methodology . They are not saying you can use their product in a way that would harm an individual . It is usually for AHUs and most show their units with a heat exchanger for hydronic systems .

See the illustrations on pages 16 - 17
http://www.htproducts.com/literature/lp-179_0417.pdf

hot_rod

Rich said:

Jells said:

So, the valve saga continues, but now I'm closer to the culprit, and its not the valve. Tenant texts this morning there's no HW. ****? There's no cold feeding that valve now!! It's not even a valve anymore, its effectively an elbow!!

Turns out both check valves on the heating loop are failing and cold water was feeding back through. When I increased the flow by opening all 3 taps the check valves would close and there would be hot water. And every time I screwed with it and left, it was working because the screwing around loosened the checks, but apparently then hours later the checks froze again and no HW once more. These are swing not spring checks, and when I tried to open the service cap it was not happening. They have to go. A question is whether the spring type is better than gate for some reason.

There's still one more puzzle piece. Why was the water feeding back through at all? The CV of the loop should be enough to prioritize the flow from the straight shot down into the tank. Can there possibly be an obstruction in the few inches of pipe from the tank to the tee? There's no dip tube on the hot, right? It's just straight from the top of the tank. Can there be a heat trap valve in there failing and blocking flow?

Henry, are you saying the mfrs of these tanks that have side taps for heat loops, and directions in their manuals for using them for heating, are selling them for that purpose without certification?

I think what is being missed here is the necessity in some codes for pump exercise at intervals so water is not sitting breeding Legionella . Some codes do not recognize this but it is effective methodology . They are not saying you can use their product in a way that would harm an individual . It is usually for AHUs and most show their units with a heat exchanger for hydronic systems .

And if the system is zoned with valves then all the valves would need to open somehow to allow every loop to exercise.

See the illustrations on pages 16 - 17
http://www.htproducts.com/literature/lp-179_0417.pdf