Caleffi 280 Thermostatic Mixing Valve

I think its correct to say my radiators are "bigger" than my boiler: there's 2100 sq ft of EDR in old cast iron radiators, and using Formula 2-2 from iDronics issue 35, that tells me I'd get (need?) over 300,000 btu/hr with an average water temp of 170F and a 70F room. However, I should emphasize that during the cold snap the house was plenty comfortable with (if I'm remembering correctly) 130-140F water temps, which is ballpark 200,000 btu/hr using that formula. That plus my massive exposed supply and return lines in the basement probably matches the 235,000 btu/hr output of the boiler. The boiler didn't run the entire day, but plenty of it (I think 16-17 hours according to the ecobee logs).

Yes, during recent service calls the boiler does cycle off, and I verified (on the control board's LCD screen) that the boiler temp during these short off cycles is near the setpoint (178-179F).

I have ordered the 130F cartridge and will give that a shot, but your previous message about the flow rates I need to get sensible delta T in my system makes me think I will probably need a different circulator. Is that right? One step up from the NRF-33 would be the NRF-36, I think. Would that be a good choice? What else could I do here?

I did use a (cheap/digital) strap-on temperature probe that I wrapped around the return pipe with some electrical tape and a piece of pool noodle for insulation prior to the install of the protection valve. That was giving me readings way below 120F nearly all the time, including at the end of heating cycles. I'm not confident that it was super well calibrated, but I would be surprised if it was 20F too low…. This is why I decided to install the valve in the first place.

regarding circulators: I think an NRF-36 fits exactly in the space that my nrf-33 currently occupies. If I find that I'm still getting (some) cold radiators after swapping out the 140F cartridge for the 130F cartridge, do you think this circulator upgrade would help?

I do not have a Y-strainer, at least I haven't found one anywhere yet.

Is there a reason you picked the PL- line of circulators instead of the NRF- line?

thanks a lot for your help! I will post again in a few days when I've got the 130F cartridge to describe my (short term) experiences.

We have two Weil Mclain WGO-5 boilers running at 1.2 gph (oil) input each, heating two gravity conversion systems with original cast iron radiators in a 4-unit condo building. We do not have bypasses, so our boilers run like yours did before you added the bypass, ie cold start, high water volume, and low supply and return temps. Typical supply temps <140, and typical return temps <120.

I've experimented with different flow rates through both systems by adding a variable speed control to each of the Taco 007 pumps, so that I can run anywhere from 10 gpm to about 17 gpm (max) through each system. Varying the flow rate will change the delta T as you would expect, but it has virtually no effect on radiator balance. All heat more or less equally, regardless of gpm.

And remember, these gravity conversion systems were piped and balanced to heat evenly even at the very low flow rates induced by gravity. Yes, later modifications (orifices installed in some valves, for example) may have changed the balancing somewhat, but I have a hard time imagining a scenario where we would have some radiators cold and others very hot, as you say, unless there was some other factor like air in some radiators. In our case, I can cut our flow rate almost in half, with no noticeable effect on radiator balancing. The only way I can get a drastic difference in radiator outputs (some cold, some hot) is by getting air in some radiators, thereby totally stopping flow through those rads.

So at the risk of asking the obvious, are you sure you didn't get some air trapped in the system when installing the Caleffi, which is now contributing to low flow/cold rads?

It's possible to have air in the system that doesn't come out with "normal" bleeding. We had one radiator that for some reason bled only water when I tried to bleed it, and yet still wouldn't heat. I called our heating company to see if they could sort it out. The guy took a 5 gallon bucket to the bleeder, opened it all the way, and filled almost half the bucket with bleed water. Along the way, a massive amount of air came out. I just hadn't bled enough water to get to the air pocket. I still don't quite understand where that air was hiding, but evidently it wasn't at the top of the radiator. Maybe it was in a horizontal run of pipe leading to the riser.

One simple way to check your system is to fully close the manual bypass valve and let the boiler run just like it used to, with no bypass. If all rads heat normally, you know there's no air. But if the rads still don't heat evenly, you'll know which ones are air-bound.

I'm not an expert either, but I do know from experience with our system that air anywhere in a radiator loop will prevent flow through the entire loop, meaning the supply pipe will stay just as cold as the radiator. There are two radiators in our building where the supply and return pipes remain cold because the owner of that condo isn't interested in bleeding her radiators, so those entire loops stay cold. I can walk through the basement and feel each supply takeoff, and when I find a cold one, I know there's air in that loop.

If the boiler runs long enough, eventually some gravity circulation will occur inside the supply riser, so the supply riser eventually gets warm, but not because there's any flow through the radiator. It's just warm water going up one side of the riser, and cold water going down on the other side of the riser. And the return remains cold.

My only guess at what happened with the air-bound radiator I mentioned is that there was an air pocket in the horizontal pipe in the basement that takes the water from the supply main and feeds it into the vertical riser. And the guy who bled that rad had to flow enough water, fast enough, through the bleeder to force that air pocket to move out of the horizontal pipe, up through the riser, and into the rad where it bubbled up to the bleeder. I can't say for sure that's what happened, but it's the only explanation that makes sense to me.

Another option is to see if you have shutoff valves where the original gravity conversion pipes transition to your newer near-boiler piping, and close off all the supply branch shutoffs except one. When the boiler runs, all flow will be forced into the one open branch, increasing the gpm to that branch and hopefully moving any air pockets. Obviously you'd only do this with the branches that aren't heating. Then try bleeding the cold rads on that branch again.

In our gravity conversion system we have 3 main branches coming off the near-boiler piping, with valves at each transition, so if needed I could shut off 2 of them and force all flow through the other one. Unfortunately I didn't know enough at the time to try that method with the one air-bound radiator I mentioned.

As @hot_rod said, our gravity conversion pipes are pitched slightly up, at about 1/4 inch per foot, including those leading to our "problem" rad. So in theory, the air pocket should have naturally migrated up into the radiator, but for some unknown reason, I couldn't get it out with the typical slow trickle flow rate that I'm used to bleeding with.

How high above the boiler is that radiator, approximately? What is the pressure on the boiler gauge?

You want at least 5 psi at the top of the upper radiator. On problem air systems you can raise the fill to 28 psi and try another purge. That helps push problem air out, sometimes. Reduce the pressure back down after this method.

There are other methods for a power purge if the boiler could be isolate, using 30- 45 psi right from a garden hose. Hook a bleed hose onto the problem radiator and let it rip for 10 minutes.

IF it is air locked you need flow, pressure, or both to push that air lock out.

OIn long loops or large diameter piping a tech will often use a purge cart, high gpm flow.

Got a pic of that problem radiator? Maybe you lower system pressure and add a better, higher flow valve at that radiator for the purge. Even a 1/8 or 1/4" mini ball valve will flow better that a coin bleeder.

Here is a portabl;e "test" radiator in my shop. When I fill it for flow tests I open that mini ball valve and it purges quickly and completely.

Sadly we don't offer this vent in North America. It is a 1" vent with a float and hydroscopic cap. So very fast venting with the two stop features.

Caleffi #504 Aercal in 1/2, 3/4, and 1" rh or lh thread.

"a ton of air every couple days" suggests something is wrong. It looks like your setup is "pumping away" from the expansion tank, which is correct. But maybe your pressure is set too low and you're pulling a vacuum in that problem radiator? What is your static water pressure, and are you sure the gauge is correct? Also, what is the height of the radiator?

PS—the link doesn't work.

sorry about that, here is a corrected link: https://digital.bnpengage.com/ebook-john-siegenthalers-top-25-0322/02-the-dos-and-donts-of-3-way-thermostatic-valves/

static pressure is in the high teens: the boiler gauge reads like 17-18, and the gauge on the fill valve reads about 16.

the problem radiator is about 18-20 ft above where the boiler sits, though its horizontally maybe 50ft away?

to be clear, there are many problem radiators (in the sense that there are still a bunch of cold ones), but the one in question is the one which bleeds a bunch of air every day or so. The other cold radiators bleed water.

Maybe an additional useful fact: most of the cold radiators that are not the one in question are all at the end of the same tee. The first 4 radiators on this tee are plenty warm, and the last 4 are basically all cold. I have tried bleeding all of the cold ones and they too just spit out a stream of cold water into my face…

It sounds like the piping is the original large-diameter gravity piping, which means there's very little pressure loss in the pipes due to friction, so the water should circulate freely and easily through the pipes with minimal pump pressure. So the piping isn't your problem, it's a combination of air and possibly reduced flow due to the thermostatic bypass valve.

So IMHO, you have two problems to solve: (1) where/why is the air getting in, and (2) a flow problem that may or may not be related to #1. But until you solve the air problem, changing the bypass cartridge isn't going to fix the cold radiators.

If the system was working fine and all radiators were getting hot before the bypass was installed, that means air wasn't getting into the system before. Something changed with the bypass installation that is now allowing ongoing "sucking" of a lot of air into the system. Either that or there was a ton of air introduced when the bypass was installed, and now it's coming out a little at a time through the problem radiator, and you haven't gotten it all out yet.

I'm not an expert, so I would ask the experts like @EdTheHeaterMan and others if it's possible that air might be getting sucked in somewhere. But it sounds like your system pressure is high enough to prevent a negative pressure that would suck air in through, say, a radiator valve.

You can add air to the expansion tank by unscrewing the black plastic cap near the perimeter of the top of the tank. That hides a Schrader (bicycle tire) valve through which you can add pressure. But don't do that until you know how much pressure increase there is when the system goes from cold to hot. In our case, it's 5 psi, so for my system, I wouldn't raise our cold pressure above 20 psi in order to keep well below the 30 psi relief valve threshold when hot. Depending on your tank size, you might have more of an increase when hot, so you may not have as much room to increase pressure.

We run 15 psi cold/20 psi hot, in a 2-story system like yours with boiler in the basement, and we don't have air problems. You have similar height and pressure, so either there's still residual air in the system from the bypass install, or air is now being continually ingested in some unknown way.

An update after a couple days with my "130F" cartridge:

(1) I never heard any of the whining that @EricPeterson mentioned when I had the 140F valve cartridge. Now I hear about 2 minutes of it at the beginning of a heating cycle. Any idea what might cause this? It does seem to go away once the valve opens a bit to the system return but it is loud enough to notice. Is there a chance I messed up the installation? I followed the steps in the instruction packet, as well as this video, very closely. I would love to make this go away if its possible… https://www.caleffi.com/en-us/blog/how-do-i-change-thermostat-boiler-protection-valve

(2) The mixed temperatures I am seeing with this valve cartridge are quite a bit lower than what I saw with my original setup. Before, I was seeing mixed temperatures (as measured by an IR pointed at the piece of pipe closest to the system inlet) of 130 - 145, with the mixed temperature reaching 130 only a few minutes after the boiler started. Now, I am seeing mixed temperatures that start at 100-110 and very slowly make their way into the mid to high 120s. I would say I get to about 120F within 30 minutes. I have not yet seen a measurement over 127F. Is this to be expected? I wonder if I somehow got the 115F cartridge by mistake. The packaging says "F29634 DN 25-32" on the first line and "55C - 130F" so its not ambiguous. I know @hot_rod has mentioned a few times in this thread and others that the 115F cartridge is probably fine for a modern gas CI boiler, but I thought I'd ask.

(3) The new valve cartridge, whatever temp it actually is, has indeed improved balance in the system, presumably by increasing the flow I'm delivering to the system. Not all of the cold radiators get warm, but a couple of them do. The "problem" radiator from a few posts up has even felt hot once or twice! At the end of a longer call for heat (before it got warm here!) I saw a system delta T (boiler minus system return) of about 35F, which is getting closer to what I was hoping for. At that point the return temp was 121F, the mixed input was 125F, and the boiler output was 156F. This was after about 2 hours of boiler operation.

I will probably still upgrade my circulator, but I thought I'd share my experiences.

Thanks for sharing that @EricPeterson. Is it safe to summarize your findings about the whining noise and its solution as: during the cold start, when the bypass is fully open and the return port is closed, the single speed pump was pushing water fast enough through just the boiler and bypass loop to create noise, and you fixed this with an ECM which pumped slower during this phase?

If I've got this right, its sort of bad news for my plans to improve things via a more powerful circulator. In this brief boiler and bypass only phase, I estimate my current NRF-33 is pumping 20 gpm, and this steps down to about 14-15 gpm once the return port is open and the pump is exposed to the rest of my system head. However, I think I should be aiming for 20-23 gpm in order to get a delta T closer to 20 on my 235,000 btu/hr boiler, so one interpretation of these facts is that this noise would become permanent under a more powerful circulator, I think.

One part of this explanation and my experience that isn't identical to yours is that I only experienced this noise after replacing my 140F cartridge with the newer cartridge. It would seem that if high pumping against a short and lower head loop is the explanation for what I am experiencing now, I should have experienced it with the 140F valve too?

Thanks @EricPeterson. I suppose the other confusing piece about this theory of the temporary whining/humming sound is that prior to even having the boiler protection valve, I never heard this sound. I would have thought that my system as a whole has less resistance than the valve itself (old gravity conversion with enormous pipes, etc) and so I think I was pumping even faster than 20 gpm back then, but obviously I didn't have direct measurement, only something approximate via noisy temperature readings and knowledge of the boiler output. My near-boiler piping was obviously a bit simpler then, too, so maybe there was less to hum? I am not sure.

In case you think this is useful information: when I had the 140F cartridge, I basically always heard swishing sounds, similar to what I hear when water goes down a drain. Not continuously, but say a few times a minute. Now I don't hear those sounds, but I do hear the whine/hum during the first 2 minutes.

I have a better temperature gauge on the way, and its going to be colder over the next few days. I'll try to take more careful temp measurements and report back what I am seeing.

I definitely have less air now after the cartridge change out, and I was careful to refill the system to pressure after doing so. Now I am not hearing any of the swishing I heard but I do hear that hum for the first 2 minutes.