Is running a system backwards a problem?

mcho

I finally found a competent heating guy in Santa Fe!! Of course he's not from New Mexico. Anyway, I asked him to confirm that my system was installed backwards and he confirmed that it was indeed completely backwards from the boiler manufacturer's instructions. Attached is a diagram from the manufacturer of the boiler.

The system is a LAARS MiniTherm II 125JVT for radiant floor heat in a slab.

My system piping is closer to the diagram on the right even though I have Entran III which requires a lower water temperature. At any rate, the system (while not exactly the way the diagrams show it) is plumbed exactly the opposite of the diagram. The single circulator in my system pumps out of the boiler and the zone valves are on the supply side of the plumbing. There is no secondary zone circulator (which might explain why the far zones do not work well).

While the house is warm enough, I keep having to replace parts that are failing, especially Honeywell zone valves. The new NATE certified tech thinks the valves are failing because of too small a transformer (I replaced that with a bigger one after discussion on a separate question on the Wall) but also because the system is backwards and it is putting too much strain on the valve motors.

Question: How big a deal is it if a system is installed backwards from the boiler installation instructions?

STEVEusaPA

Too small a transformer will eat up zone valves. The wrong configuration probably not. Pumping into the closely spaced tees is probably not helping.
Why can't this be corrected?

Paul48

What is the boiler? How are the zone valves controlled? How many zones? With no secondary circulator, you're getting convective flow at best. As Steve asked...why aren't you correcting it?

mcho

@STEVEusaPA I agree and I installed a 75VA transformer in place of the 40VA.

@Paul48
That was my reason for asking. Does it need to be corrected? What happens if it is not corrected?

The piping is so wrong that it would have to be completely redone. Since the existing boiler has been very reliable and is so simple even I can fix it I am reluctant to change it.

However the boiler is almost 30 years old so if this has to be corrected I'll just go ahead and get a new boiler.

mcho

@Paul48

OOOPS I did not answer your questions.
LAARS Minitherm II 125JVT
Zone valves controlled with thermostats in zones
7 Zones
Honeywell zone valves V8043E1012

Paul48

The diagram show the circulator pumping into the return. Are you saying it is pumping out of the supply, or out of the return? In other words....is it actually backwards, or is the circ placement wrong?

Paul48

Is there actually a loop(primary) formed at the boiler? If so, I can't see how the system would work, at all. And how it wouldn't just bounce off hi-limit without a secondary circ.

mcho

@Paul48 Yes it is literally backwards. One pump is pumping out of the boiler outlet directly (about 3 feet) into the zone valves, going out to the zone loops and then coming back to the inlet of the boiler.

It should be going out to the loops with a pump on the secondary side and returning through the zone valves back to the boiler inlet through the inlet pump. What I have is the exact opposite flow without a second pump. The zone valves are closing (when they need to close) against the higher pressure of the pump instead of the lower pressure of the return loop.

Paul48

The boiler itself has 2 ports... a supply and a return. Are you pumping out of, what should be, the return? Page 6 in the manual

mcho

@Paul48 Fluid dynamics is extremely complex and difficult and its hard to predict why the system works. I never studied that topic myself except what was required when I was in college. I think that's why I am having a hard time understanding this.

But does it actually matter? How big a deal is it? Are things being damaged? The house is warm enough and the system seems to work. My technician of course has a conflict of interest because he wants to sell me a boiler so I need another opinion from some one without a dog in the fight.

mcho

@Paul48
The single pump pumps out of the outlet of the boiler into the zone valves on the secondary side about 3 feet away. There is no pump pumping into the inlet of the boiler. All the flow in the system is either from convection or from the pump on the outlet of the boiler.

Paul48

OK.......Then the direction of flow through the heat exchanger in the boiler is correct. Many times manufacturers want the circulator pumping at the boiler(return side), to prevent the pump from cavitating, and destroying itself. If, in 30 years it has not been a problem, I wouldn't worry about it. I would address the lack of a circ on the secondary side.

hot_rod

I would highly recommend separating that rubber tube from all the piping with a plate heat exchanger and non ferrous components.

Also a buffer tank would help that single speed, low mass boiler. As you zone them they tend to short cycle badly.

A buffer tank would add some mass and also double as the hydro separator.

Contrary to what some suggest that boiler does need to have return protection, it should not be run in condensing mode. Either with a thermostatic valve or a smart control running the boiler and pump.

mcho

OK I am hearing its OK and not the end of the world to have all the components installed backwards. I just need to add a pump, ensure the manifolds are non ferrous (they are copper -everything is copper including the boiler heat-exchanger is what I have read) and I need a buffer tank (which is not possible -there is no room). Additionally I need temperature controlled mixing valves as called for in the low-temperature configuration I have.

Thanks for your help guys!!

mcho

@hot rod
If this is necessary then I will go ahead with a new boiler because there simply is no room. The existing system is shoe horned into a 5-6 square foot area. The only way to add room is to sacrifice the coat closet by the front door and the Boss is never going to let me do that. I can't bump out the wall either because it is an outside wall on the front porch and she won't allow that either.

Everything touching the tubing is copper from a copper manifold. Is that for hydraulic separation? Will the copper be good enough?

The technician turned the boiler back down to its lowest temperature. I asked about a temperature controlled mixing valve (the low temperature diagram requires two). He thought the manual mixing valve I installed would work just fine but I don't agree. That can't work without sensors.

So what I am hearing is that going backwards is OK as long as the flow direction in the boiler is correct, So I don't need to rip out all the piping and start over. But I should make the changes that Hot Rod and Paul48 is suggesting which would be cheaper and very do-able in the near term.

Mark Eatherton

Look at the zone valves. They have arrows on them indicating proper direction of flow. If the water is flowing against the arrows, that particular valve HAMMERS when it closes (BANG BANG BAng bang) if there's flow. (i.e. 2 zones calling, and one closes)

If in fact the flow is going through the boiler backwards, it will cause the boiler to short cycle, because the operating thermostat normally "watches" the return so that the mass of the distribution system and the connected loads will "buffer" the boilers operation. This is normally set for around 160 degrees F.

The high limit, is required by the boiler code to be installed on the boiler outlet, and again if it is running backwards, this could create a dangerous over temperature condition. If the high limit is set for 180 degrees F., then the system discharge could exceed 200 degrees F. if the operating control were to fail, which they do.

Your technician isn't doing the boiler any favors by turning it down. The heat exchanger will condense, and cause the heat exchanger to deteriorate from the acidic corrosion. You will eventually experience roll out of flames at or near the burner assembly drawer due to the flue gas passages becoming blocked.

If you happen to be so lucky as to have a roll out switch in a position where it can see the roll out, the boiler should shut down. If you are unlucky, you could get carbon monoxide poisoning. Waking up dead is not a good way to start the day... Make certain you have working CO detectors throughout the home.

If you look up into the combustion chamber between the burner tubes with a mirror when the boiler is running, you will possibly see "clinkers" glowing on the copper finned heat exchanger. That is an indication that the boiler needs torn apart and the heat exchanger cleaned at the local car wash.

Entran 3 had an EVOH oxygen barrier as a part of its construction, but it will still degrade and become brittle, requiring eventual replacement. Be VERY careful if you have to move it.

This just goes to show you, that even with everything all screwed up, hydronic heating systems can still deliver comfort, albeit inefficiently. Hydronics RULE!

ME

Zman

Do you have pictures of the boiler and piping?
Those mini therms are pretty particular about flow.

mcho

@Mark Eatherton WOW Mark. I see I still have a great deal to learn. And yes this is why I turned the furnace up and put in the mixing valve. But the Technician said that was not necessary. The condensation is so bad that the damper is stuck open and when it gets windy here the boiler shuts down because the rollout switch (new - I replaced it) has noticed the flame roll out. I have had to replace the exhaust stack twice until I started learning hydronics. I'll put it back the way I had it.

I do want to mention that the flow through the boiler is in the correct direction its just that pump is on the outlet pumping out with the control valves instead of on the return as in the diagram. The valve flow is in the right direction for that configuration.

But I think you are convincing me that I need to buy a new boiler, and I need to check that this technician actually has the hydronics NATE cert and not just the basic.

@Zman I'll send pictures tonight. I have to teach today so I am stuck at work.

mcho

Here are the photos.

I was thinking of a getting condensing wall hung boiler but I am thinking that I don't need 90% efficiency since I have a passive solar house. Now that I tightened the house the house only loses a few degrees during the night even if the boiler is off, I keep the house at 78 (I am old!) and the bill is never above 200 a month (including a giant hot water tank and oven). Not much of a concern.

The technician wants me to buy a Burnham Alpine. However the mini-therm has been reliable for the 20 years I have lived here albeit a few minor parts I had to replace (all the troubles have been with the rest of the system). I have a thorough understanding of how it works and can fix anything on it. Seems like a bad idea to buy a complicated boiler I will never be able to fix myself. I am just going to buy another Mini THerm II. Strikes me as more sensible.

Anyway here is the front half of the system. The other 4 valves are under the bathtub in the guest room. Notice the plumbing between the outlet and inlet with ball valve. I put that in years ago! Not bad sweating for an amateur! I saw in the diagram its supposed to be there and it wasn't so I decided to put it in so I could run the boiler hotter. At the time I did not know you could buy a valve controlled by temperature.

Zman

If you decide to go with another mini therm, don't do that to it.
You would want to install it with 2 circs in a primary secondary arrangement.

The boiler needs to run at high temp(160 or more). Your house will be more comfortable and the tubing will last longer if you mix the radiant temp down to a much lower temp and use outdoor reset (90-120 degrees will probably do it).

There are quite a few ways to do this. I would probably use a taco I series mixing valve with outdoor rest and anti condensation built in.

Do be sure to replace as much of that flue as you can and carefully inspect any you reuse. Your boiler and flue are done...

Mark Eatherton

Death sweat.... The guy must have read "Pumping Away", or at least parts of it.

ME

mcho

@Zman Thank you!! Thats what I thought too but the NATE certified guy said that outdoor reset thermometers were only for baseboard type heating and that one pump would be enough!! I was pretty sure he was wrong. I guess I am back to doing everything myself! Darn! This is not how I want to spend my time.

Oh and no worries, I'm not penny wise. I will be replacing everything that has any corrosion. The parts are quite inexpensive when you don't pay 6 times the retail price. I am old but I have a very comfortable income.

I have the furnace back up to 160 degrees. I hope that is enough. I am worried about the tubing until I get the TACO mixing valves. If I do the work myself it will be exactly in accordance with LAARS instructions plus the optional outdoor reset control which they show how to wire.

mcho

@Zman:
Do you think that if I called TACO they would help me figure out correct parts to buy and advise me or do they not talk to homeowners?

mcho

@Zman: Nevermind I figured it out. TACO instructions are very good!