Stadler radiant heat loop always circulating

Bart56

My daughter's older home has a Stadler radiant heating loop in a small portion of her oil=fired hot water baseboard heating system. The main hose is on one circulator, the DHW is on another, and there are a supply and return to the Stadler system pictured below:

That circulator pump is always running which I believe is not correct. All year long, it runs no matter the temperature outside because the 120V line is not switched. The little silver wire at the top right goes somewhere that she cannot find - which I would have suspected is a thermostat somewhere.

Recently, she had her boiler serviced, new nozzle (slightly hotter .85 gpm than the old .65 gpm . the burner specs called for .85) It was working fine until this warmer weather..

On the first mild day (40's) her oil burner fires for short time, then stops for about 20 minutes. Then fires up again. The hydrostat shows it firing on at 125 deg and off at 145 deg, but latent heat will rise to 170 deg. Min tem was set to 135, max was 170.

Besides wasting a lot of oil, the hot water also travels into the main heat zone without being called so the first couple of radiators in the 1st floor loop and 2nd floor loop get quite hot.

My theory is that the radiant floor cools the burner to 125 and it kicks on to heat the water for the floor, but after it kicks off the hot water in the boiler will also rise into the main loop without being called. The house was getting to 72 degrees on these warm days.

I'm planning to visit her and try to understand why the Stadler circulator pump is always on, but she has no user/install manual or papers on it - it came with the house. I was also thinking of turning off the hydrostat's low temp setting (it's either OFF or 110 deg and higher. It's set to 110 right now)

So if someone could steer me to either some documentation or just some advice on what else to check, I welcome any and all information - especially on the Stadler system.

Thanks in advance.

Bart

mattmia2

my guess is the cap tube you can't find the end of goes outside somewhere for outdoor reset so the loop temp is set by the outdoor temp. the constant circulation isn't super unusual for a radiant system.

is the main loop also radiant?

i don't see why the boiler would rise to 170 from a low limit call if the low limit is at 125 unless it has the differential set very high or a heat call is bringing it there

Bart56

No the radiant is only a 12x12 area with a concrete floor. The rest od the house is served by a single loop that splits into 1st and second floors somewhere in the wall/ceilig of finished basement. The loop that feeds the first floor runs exposed from the finished basement ceiling with no radiator vanes in the basement.

The burner cuts off at 135, but latent heat (I'm guessing) causes the water in the jacket to continue heating then slowly falls off while the radiant heat continues to run.

I'm thinking of lowering the nozzle back to .65 gpm even though the burner calls for a .85 in the manual.

We pulled the 1st floor thermostat so there was no heat call during all of this and no zone lights on the Taco sr0593-4 were lit.

Thanks for responding so quickly. .

hot_rod

Follow the flex electrical conduit to see what powers the pump. It could be as simple as a stuck relay.

Why was the burner nozzle changed? Was the boiler not keeping up with the heating load?

Bart56

The BX flex wire goes to a live ceiling box. No connection to the boiler. I hope to confirm this tomorrow. As for the nozzle change, when the tech came because the burner kept needing a reset - the flame would not start reliably. He looked at the burner manual which called for a .85 -80B so that's what he put in.

I asked my daughter to lower the hi temp to 160 and the Lo temp to 110 last night and the system seems more stable, but house temp is still at 67. It is set for 62 all the time.

I'm still a little perplexed on why the house loop gets so hot when it's not calling, and how the stadler should be wired like a normal zone (thermostat and relay - there's a free circuit in the Taco 503-b).

Thanks very much.

Alan (California Radiant) Forbes

The pump is always on because it's directly connected to non-switched line voltage.

And the air temperature sensor is there at the manifold when it should be in the heated space, no? During the winter, it never warms up and keeps on heating the space.

The solution - at least for the radiant floor - is to install a thermostat in the room(s) with the radiant heating and wire it to a transformer relay next to the manifold to control the pump. Either wired or a wireless thermostat.

As far as the main floor overheating, it sounds as though there's gravity flow when the thermostats and pumps are off. There should be check valves on the discharge side of the two pumps and maybe even check valves on the returns.

mattmia2

so the "loop" isn't a radiant loop, it is fin tube baseboard?

then flo checks or zone valves not working properly are the issue there if the fin tube is hot. Still doesn't explain how the boiler gets to 170 unless the radiant is essentially not losing much of any heat and the mix controls are causing it to just circulate mostly loop water and very little boiler water.

Bart56

No it's not fin tube, it's radiators (the house dates back to the 40's and fairly sure the radiators were built in at that poin - but not certain.) The loop is iron pipe which tells me it's pretty well dated and may have been a steam loop way back in the day. The connections to the boiler were made with copper pipe, crimped joints sometime before she bought the house - maybe 10-15 years ago?

Yes - this just started happening when the milder weather came in, so the floor is probably not cooling off very quickly and the main house thermostat is not calling because she keeps it at 62 deg.

I agree on the gravity flow scenario. I'll look for check valves on the main loop. There appears to be a check valve on the supply line to the Stadler upper manifold on the left in the pic above.

@Alan - that air sensor thermostat above the manifold will control the temp of the loop (we checked) but even set to '*' (the lowest setting snowflake) the loop temp is still 80 deg. I'm going to call Stadler to see if I can get an install manual to better understand how it is supposed to work. Unfortunately, I don't know the model so I'll probably sound like a complete idiot.

Thanks for the help - all of you. I'm going to try to map out the system and get a schematic together for the future.

hot_rod

It would be unsual to haver a circ wired just to a hot feed? The only disconnect is a breaker? Is there one labeled as radiant pump?

If not that junction box may be controlled by something else. Especially if this condition, pump running constantly, just started?

Need to dig deeper.

The white control looks to have two cap tube sensors. It is attached to a 3 way valve, which could bypass or that heat from the boiler loop. Does that get adjusted ever to regulate temperature to the heaters? I don't see a need to run that circ all summer.

mattmia2

constant circulation in the us in residential is unusual. in europe not so much. probably built on the theory that we use the odr to cover the heat loss at any given time so why do we need to turn it off.

hot_rod

Stadler evolved into Viega. Early on it was called Stadler-Viega. I'll bet someone old :) at Viega has access to those early application, installation and operation data files.

Although you may learn more just digging into it.

Rich Trethewey was an early Stadler adopter he knew Joe Fiedrich who imported the brand.

Try RST Thermal, the Trethewey rep firm. Maybe they rat-holed some of those old manuals?

Bart56

@hot_rod The round white control above the manifold setup will control the temperature of the loop by letting more of the heated water through instead of recirculating it. So I think the answer to your question is yes. The circulator should act in conjunction with that need but I'm guessing it was too complicated for the original installers? Dunno.

Since there is an open zone on the SR503-4, I think the best solution is to put a T-stat in the room with the radiant floor, but that room was an addition sitting on a concrete slab. Access is crazy hard to fish a T-stat wire IIRC. That's one of the questions I will try to answer tomorrow after backing out the .85gpm nozzle and installing a .65 gpm.

For the time being, I was thinking of temporarily wiring the Nest t-stat in the main house to call two zones by jumpering Zone 2 and 1 together in parallel (R-R, W-W. This issue is not knowing how much current it takes to close a relay in the 503-4. If I parallel two zones, I double what the Nest t-stat sees. I read somewhere that one t-stat connection on the Taco box will supply about a half amp and that the Nest is good for 3 amps. Any thoughts on this?

@mattmia2 I agree. That circulator should not be running all the time.

You folks are great to hash this out with me. Thanks.

Bart56

@hot_rod - yeah - Rich Trethewey was a gem and always found the latest tech, but I'm going to try to wrap this up asap. No sense getting the stars involved LOL!

mattmia2

There are a number of wireless t-stat systems for the addition. Just make sure they don't forget about the batteries and freeze up the radiant. I meant that someone probably thought we just size it properly and we don't need to have a thermostat, it just adds what it needs to cover the loss so it should never overheat.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1845569#Comment_1845569

It could make for some good theater, radiant then and now.

Bart56

@hot_rod - you'd be proud of me. I sent RST Thermal an email asking if they might have some documentation. LOL! We'll see what comes back…

Alan (California Radiant) Forbes

The power for the pump could be connected to a "Summer-Winter" switch in the mechanical room.

Bart56

Thanks @Alan (California Radiant) Forbes . So you're saying the floor is giving up about 2 * 150 * * 20 or about 6000 BTU/hr at 20 deg delta and we're burning 10000 BTUs so the extra 4000 is going into the main loop or lost to the basement space? I know it's not actual, but the example is eye opening.

Alan (California Radiant) Forbes

https://forum.heatinghelp.com/discussion/comment/1845656#Comment_1845656

Maybe……….but I'd say the main things is that the house is uncomfortable. Rein in the way the heat is controlled and you will make your daughter more comfortable and reduce her fuel bill; major points for papa. Someone did their best to install the system that's there and now you will clean it up.

hot_rod

I think what you have is a true constant circulation system., for that circuit.The pump is enabled at the beginning of the heating system. Somewhere there is a means to shut it off. It would be unusual to have an 80W pump on a circuit and breaker of its own, but?.

Temperature to the system is typically provided by a boiler or source that modulates its temperature. If it was a RST design they often had Viessmann biferrel boilers. This was a high mass boiler that could handle small two loop zones like that pretty well.

Since you have cast rads, there must be a mixing device, for the radiant zone it could be built into the 3 way valve if it has two sensors connected

You may have a boiler that is oversized which can lead to short cycling, and inefficient operation. Possibly it is running a fixed temperature which can also increase cycling.

If only that two loop radiant is running, expect the boiler to cycle often.

It would be helpful to do a heat loss cal as the home exists, see how the boiler output matches.

Then calculate the output of all the radiators to see how that matches the heatload. Any history from previous owners as to how it performed in the past would help

Bart56

Update: The radiant floor circulator is wired to an old box in the ceiling with a constant hot. It also feeds the lighting circuit in that room plus something else buried where I couldn't find it. So yes, the circulator runs all the time.

I checked with Taco, and they tell me I can jumper 2 zones for the Nest to control both, but I'll need a C wire. So if the house stays comfortable doing that, maybe I will.

I changed the nozzle to a .65 gpm so it runs a little cooler and the latent heat isn't quite so hot rising into the house. And no, there s no backflow valve on the main house loop so that's why it is getting so warm upstairs. It's a pensotti DK2-4 boiler which called for a .85 gpm nozzle but it is too hot.

One thing maybe you can help me with: The boiler's aquastat seems to automatically kick the burner on at 100F, then shuts down at 110, and the jacket water rises to 135F before slowly dropping after installing the .65 nozzle. Should I leave this behavior or make it so that it only goes on when calling for heat? I realize the radiant circulator is pulling the heat out slowly now that it's on the lowest setting. The radiant loop was 70F. Sooner or later it will pull down the jacket temp and the burner will kick on. It takes about 20-30 minutes between cycles.

I am also thinking about putting a thermostat in the sunroom with the radiant floor. But I need to think thru it. If the sunroom gets cold, it will start the circulator and the boiler, but the temp is so low, it will be short cycling by hitting the aquastat max temp then lo temp, etc., as @hot_rod points out I'm not sure I want to run it this way.

If I use the Nest for both the main and the radiant, I would hope it only goes on when calling.

I could do either way, but the Tstat in the sunroom feels like it would waste more oil.

Suggestions?

Edit: I thought of a third way - just put the circulator on a thermostat. This way the call for heat will be only when the loop needs more heat. Not when the thermostat is calling. I've got an old 24V Honeywell relay. I can put it in a deep box but would need to run 24 VAC to it and the T-stat. Doable but not sure if bettter than having the Nest control both zones. Hmmm…

Alan (California Radiant) Forbes

Can you take a picture of the wiring inside the Taco box and post it here?

hot_rod

when you put a small load on a boiler like that, it may satisfy the heat call before the boiler runs long enough to warm the return above 130. You could easily try that by just running the radiant, measure temperature at the boiler return, and time the run cycle.

I don’t know that N would be my thermostat of choice, they don’t seem to get along with hydronic controls so well.

Did you find the circuit breaker or fuse that controls the J box? I’m not sure why it would be connected to a lighting circuit. Are things labeled in the breaker or fuse box?

I think you are going to want to shut that pump down in the summer. 80W running continuously for no reason. You or an electrician could add a junction box and a switch in that electrical flex.

A pic of the piping at the boiler may help determine why it heats when there is no call.

mattmia2

Like @hot_rod said you need to get the boiler hot enough that it doesn't condense. I'm not sure that is the same temp as for gas, i think it is lower for oil because oil contains less hydrogen.

Bart56

@Alan (California Radiant) Forbes

Tough to see details, but Zone 1 is open. Zone 2 is main house and 3 is indirect DHW with priority set. Not sure what you're looking for but lmk if you have questions.

Bart56

@hot_rod The Nest has been working fine as a 2-wire for several years. The suggestion from Taco support is that I could parallel zone 2 and 1 but I need a common wire for the Nest. So about 15 feet of 3-wire t-stat wire should do the trick. It's nearly right above the burner - easy to pull down using the old wire.

The Reillo burner is called out in the Pensotti boiler manual as using a .65 gpm for the DK2-4. So I think finding that explains why that was previously in there. It's not a condensing boiler, I know. Are you saying that is the reason why the boiler stays at 100 deg or above?

The pump looks like it's rated at 65W from the picture, but doing the math, it's about 14KWh per month which at $0.30 per Kwh is about $14 a month. That's a reason to shut it down when not needed.

I don't find the breaker for that circuit that the circulator is tied into. No label for it so I'll have to find it using my foxtail tracer. I do plan to separate it from that box - it just depends on the solution I end up with.

I don't have a picture of the piping but I can tell you that there are no flow check valves on the returns from the DHW or main loop to stop the rise of hot water into the main house.. The radiant has a flow check valve as it enters the upper manifold.

Bart56

RST Thermal got back to me and will take a look through their archives next week for Stadler documentation.

Thanks for the support.

mattmia2

are there flo checks on the supplies to the radiators?

Bart56

Interesting question. They are all covered half in wall so ill ask for a picture from underneath

Alan (California Radiant) Forbes

I wanted to see the wiring on your Taco box to see if the “Isolated End Switch” terminals are used - they are. They probably go back to your boiler (T-T terminals or wires) and will tell the boiler to turn on when there’s a call for heat from one of the two thermostats. I say probably, but the T-T relay at the boiler could be jumpered to keep the boiler always on and ready to heat the radiant floor.

hot_rod

I don't see anyway for the radiant module to call on the boiler, so?? Keeping a hot boiler to supply two loops to a small radiant will certainly cost some $$

A pic of the boiler piping might help see what the options are.

Bart56

https://forum.heatinghelp.com/discussion/comment/1845916#Comment_1845916

That white wire is going to the aquastat T-T contacts. I was thinking the aquastat was firing it at 100F on it's own since it will fire without any zone 2 or 3 heat call. Make sense?

mattmia2

https://forum.heatinghelp.com/discussion/comment/1845916#Comment_1845916

i thin it is a triple aquastat with a low limit that keeps the boiler always hot.

Bart56

https://forum.heatinghelp.com/discussion/comment/1845935#Comment_1845935

I agree - that's what I'm trying to change but what's the best way to do so? I asked my daughter to get a pic but I don't think you'll see anything surprising there. I'll try to label which pipes are which but may not get the pic till tomorrow.

mattmia2

oh, my earlier question. i didn't mean flo checks on each emitter, i meant at the boiler where each ci zone supply branches off the boiler.

Alan (California Radiant) Forbes

https://forum.heatinghelp.com/discussion/comment/1845935#Comment_1845935

Is there no way to get a thermostat wire from the radiant module to the boiler?

Bart56

https://forum.heatinghelp.com/discussion/comment/1845975#Comment_1845975

The "module" is totally non-electric. The manifolds and temp sensors/controller have no contact leads. If I put a thermostat in the radiant room, then yes I can run the circulator off the remaining zone 3 on the Taco. But I'm having second thoughts about the slow room response time and how long the boiler will cycle after a call for heat.

I think the better approach is the run zone 2 and 3 in parallel controlled by the house thermostat. The radiant room is a part of the house with no door or walls (i.e. open floor plan) So it makes sense to me to treat it as one big zone.

Truth be told, I would have liked to see the main floor and second floor as separate zones but this was decided long ago and the walls and ceilings closed. So I think piggybacking the radiant with the main house would be more efficient because:

1. The radiant circulator would only run when the house actually needs heat (when the main thermostat calls)
2. The burner would already be firing to satisfy the main house heating demand
3. It would eliminate independent cycling just for the radiant loop
4. The system would operate as a unified heating solution rather than competing zones

This approach essentially "piggybacks" the radiant heat on the main heating calls, which should reduce both electricity usage (no separate pump operation) and oil consumption (no additional burner cycles). The radiant floor would effectively become an extension of the main heating system.

I think it's worth a shot and would cost next to nothing to implement to find out.

@mattmia2 There are no flow check valves in the main loop (nor the indirect water heater loop) that I can see.

Non near any radiators either. Back in the day, I think they designed systems to use that gravity feed effect of the residual hot water.

Alan (California Radiant) Forbes

The problem with running the radiant along with any radiator zone is that they heat differently. The radiant floor will take longer to heat the room and when the main floor thermostat is satisfied, the radiant room will not have reached setpoint.
My original suggestion to install a thermostat in the radiant room and connect it to a Taco SR501 (transformer relay) at the manifold to power the pump still holds. To prevent short cycling, don’t run the isolated end switch in the SR501 to the aquastat. There will probably be enough heat in the boiler from the other zones to heat the radiant.
And I don’t understand your logic in combining zones 2 and 3.

Bart56

@Alan (California Radiant) Forbes I get your reasoning.. You're saying just let the thermostat in the radiant room turn the circulator on and off but not the burner. This is how it heats the loop now, the circulator runs 24x7 but the burner kicks on when the jacket heat falls to 100F. So I accept that it would cut down the wasteful circulator current.

On the other hand, this room is an open part of the house. For the past week, the floor was turned off on the temp control above the manifolds and the radiant loop stayed pretty much at 70F. The house was plenty comfortable including that room. The layout of the house has a 10' wide x 15' long kitchen with one end open to the living room and the other end open to the radiant room. I know they heat differently and the floor's slower rise time and lower temp, as well as the longer heat radiating after the call. But most of that heat travels into the house (and vice-versa) as well as outside through the windows.

So I can easily try the piggyback method and then try the separate T-Stat method and see if she can FEEL the difference (besides her electric and oil bills). It's easier to implement too. There's not much wall space in the radiant room to properly situate a thermostat.

I hope this explains my reasoning better. If you think there are cost efficiency differences, I'm all ears.

hot_rod

I would say if the radiant zone is basically the same room or space as the kitchen great room zone, then keeping on one thermostat/ zone makes sense. The red knobs on the manifold would let you do some balancing if the radiant 144 sq ft is over-heating.

Since the info has been dribbling in, it is tough to come up with the best fix. It looks like zone 2&3 will call on the boiler, based on the relay box wiring. So one heating zone and one for the indirect?

I'm not sure why the nozzle was switched back and forth? If the manual calls for the .65, what was the reasoning for the .85?

All in all I don't see any major problems.

As far a heating cost, start looking for ways to upgrade the structure. Have an energy audit done, blower door and infrared scan. That could be the biggest win for lowering heating costs.

Bart56

https://forum.heatinghelp.com/discussion/comment/1846073#Comment_1846073

Sorry about dribbling info to the thread. I comes from getting all the great questions and thoughts over a period of forum days. My thanks to all of you for helping me think through this.

The nozzle was changed when the boiler manual spec'd it as .85 in one place then later called out .65 for riello burners specifically. I thought the .65 was a mistake causing the burner to reset a few months after the tech replaced the nozzle. I read that manual several times and only saw it late this past week. My bad. I caused the overheating but the reset issue was gone. Now it's at .65 and the reset issue is still gone. During this, the constant circulator for the radiant floor got my attention and is now my current objective to save her some $$.