modcon boiler not reaching set temperature

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Old 11-11-11, 10:13 AM
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modcon boiler not reaching set temperature

hey all,

I have had a slant fin b200 natural gas boiler for aboutr a year plumbed with a 2 pipe primary/secondary scheme. I have recently run into some problems. It started with 2 radiators not heating. Those radiators are fed from a branch that feeds 7 raditaors (4 of which have no flow control valve). The branch is fed from a 3/4 pex tube that come from a manifold. Each port of the manifold produces 2gpm max. I figured that the 2 gpm simply could not feed 7 cast iron radiators. I had a friend (mechanical engineer) come in and he added t-fittings to the feed and return line and connected the 3/4 pex that feeds the afformentioned branch to them. This seems to have worked as now all the radiators in the house come on and are fairly well balanced.

A new problem has now developed. When the boiler runs it will not get past 140f unless I restrict return flow to the boiler. I am assuming the problem is that too many gpm are flowing through the boiler and not allowing the boiler to heat the water. At the same time the return water temperature is higher than it should be. With a supply temperature of 140 the return temperature will be ~135. This is not good because it is pushing the boiler out of condensing mode. I am assuming the problem is the primary/secondary plumbing. When I restrict the secondary (return) the primary pushes more water down into the secondary/return basically pushing just heated water into the boiler's return. I am wondering if I should just remoed the primary/secondary system?

What I did notice is that slant-fin mandates the use of a Taco 0011 circulator pump on the return side. The installer, however, used a taco 1400-45 pump which flows 25gpm more. I am wondering if my system is just over pumped....There are two pumps, return pump is the 1400-45, supply side pump is a taco 0010.

any insight is appreciated!
 
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Old 11-11-11, 11:30 AM
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Hello,
What happens if you turn down the temperature setting for the boiler?

Certainly, the more flow the lower the delta T betwee the inlet and outlet.

There is a table 2b, for indirect heaters on page 26 that show various DeltaT's for different flow rates.
The 1400-45 is in the table, and it might too much pump, but it depends on the head loss.
It's for indirects but gives an idea.

http://www.slantfin.com/images/stori...bcat_ba_40.pdf

The manual says the boiler circulator is supplied with the boiler.
Was this the 0010?

Lots of pictures will help the knowledgeable folks here to assist you.

Peter
 

Last edited by NJT; 11-18-11 at 04:24 PM.
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Old 11-11-11, 01:48 PM
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hi, thanks for reply.

I made a mistake. The Taco 0011 was for the smalle b120 boiler, I have the b200. Here is what the manual says "0013 for B-200A" So I need the 0013 not the 0011....the difference is 2gpm so 33 not 31 which is still a lot less thatn the 0014's 55.

It says it came with it but mine did not, unless the installers kept it and gave me a 0014 thinking I need more flow. I can only assume they mandate the 0013 because they want a certain amount of pressure/flow through the heat exchanger.

I should note this. I partially closed the new 3/4 loop I had installed. With it about 80% closed the boiler went from 140 to 165 degrees. That, however, is internal temp...the manifold read ~140 on the feed and ~110 on return. The problem is that the boiler's return reads ~134. Seems to me that the primary/secondary is allowing hot water to affect return temps.

Next time I am down there I will be sure to take pics. I can't go to the basement very often (2 floors down) because I had a knee osteotomy surgery a few weeks ago. I can't put any weight on my knee for another 3 weeks. It is a tiring challenge to get down there!

thanks again
 
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Old 11-11-11, 10:27 PM
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Well it turns out I have the proper pump. It is a 0013 and the supply circulator is the 0010. I am wondering if maybe the 2 pumps just make too much flow for the boiler. I believe the 0013 has 31 head-feet and 35 gpm and the 0010 is not far off of that. With that much feet-head and ~60gpm it seems like quite a heavy flowing system.

I have another question. The boiler came with an outdoor sensor for outside reset control or as slant-fin calls it, weather compensation. I have set it up and it works quite nicely. There are two control options for this. You can either control the boiler just with the outside sensor or you can select outside sensor and thermostat.

When I originally set it up I used "just sensor". It came on alright and heated the water but none of the circulator pumps came on. I am assuming this is because they are controlled by the taco zone valve controller and the thermostat. I switched the control to outside sensor and thermostat and everything is working well. I would really prefer to run the system with just the outside sensor. The thermostat is mounted in a poor location, near the kitchen in the living room with the fireplace. The fireplace cannot really be used because it will shut off heat to the rest of the house. Would it be best to wire the pumps so they run all the time? Could I wire the pump so that it comes on whenever any of the zones or dhw is on? I wondering if the boiler has a wire connection just for this scenario.
 
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Old 11-12-11, 11:05 PM
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Apparently the installers did not install the boiler to the exact specs in the manual. The diagram in the manual indicates that there should be an isolation valve above the pump between the pump and the closely spaced T's, and there should be a flow check valve between the pump and the boiler. Neither of these are plumbed in.

I must admit that I don't know how these things will help. I am assuming that the isolation valve just lets you close down the entire return (maybe even the whole supply and return since they are connected), and the flow check valve limits regulates the amount of flow through the boiler. Is this correct?

I may just swap the pump out for the taco 0013-f4-1ifc which has an internal flow check valve installed. I am also wonering if maybe the supply side circulator pump is too big. I read a few articles that state the old gravity systems are fairly free flowing with minimal head loss. They suggest that too big of a circulator will cause the water to skip through the radiators and the boiler. I am thinking maybe I should install a smaller circulator pump that flows less GPM...maybe even a speed-control pump.
 
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Old 11-13-11, 07:37 AM
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Hello Silky,
The flow checks keep heat from going to waste when things are not running, otherwise, they make no difference.

I'm guessing you have read this, about gravity conversions:
Heating Help

Can you describe exactly what type or radiators there are, 2 pipe, one pipe, inlet out on the same side or opposite etc.?

Peter
 
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Old 11-13-11, 08:47 AM
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Silk, can you provide a diagram of how this system is piped?
 
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Old 11-13-11, 11:33 AM
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thanks guys, I appreciate the assistance.

I don't believe I have read that but I will when I get a minute. I read a bunch of articles and threads i found by searching. I must admit that I went into this knowing nothing about hydronic plumbing styles but figured since the installers around here seem useless I better learn! The gist of what I read was that gravity feed conversions don't need much pumping because they are inheritnly less restrictive so headloss is low. The 0010 pump that pushes the manifold flows something like 32gpm at 31 feet of head. The primary and secondary loop pumps put out a combined 61gpm with 31 feet of head each.

The radiators are 2 pipe cast iron with the pipes on the same side. Some of the rads have no vales...smallers rads near doors or in washrooms. I am guessing it is because you want those areas warmer. One of the problems I originally had was 2 radiators were not working. These radiators were fed by a 4" trunk line that fed 7 other radiators. The trunk line was fed from a 2gpm 1/2 pex output from a manifold. 4 of the 7 radiators there have no valves to control flow so I figured the problem was that 2gpm was not adequate to supply 7 rads. That has been rectified.

This is my tentitive conclusion:

Before I had weak flow through the return side because the manifold was severely limiting the gpm in the return loop. This caused more primary side recirculation (just heated water flowing back to the boiler return from the closely spaced t's). This meant the boiler heated up rapidly to the full 185 set point because it was just cycling warm water. Since I rectified the radiators that were not coming on the boiler is struggling to produce 140*. I believe this is because of increased flow. The more free flowing return is not overwhelming the boiler. ie. too many gpm's flowing through the boiler not allowing the boiler to heat the water. Basically before there was too much restriction, now it is too free flowing.

I am not sure but could the system be working correctly? The point of modulating boilers is to restrict output temperatures to keep a delta-t of ~20 correct? It seems that whatever the supply side temp is the return side is between 19-25* cooler. When supply is 150 return will be ~128-131.

NJ TROOPER

I have some pictures of the pipes I can upload and I will make a simple diagram of the install and the way slant-fin wants it.
 
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Old 11-13-11, 01:25 PM
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If piped properly piped p/s systems create what we call hydraulic separation. What this means is the flow of one pump will not affect the flow of another pump. So you thoughts of combined flow is not correct if the p/s is piped properly. Your pic's and sketch will show this.
The backward flow between the boiler tee's is a result of the flow in the boiler piping greater than the flow in the system. This can be normal or maybe not. It is normal when all is correct and the system is zoned and not all zones are open. What does not go out to the system will flow back to the boilers. When everything is not correct like piping, pump sizing, boiler sizing etc.
When boilers piped with p/s are over sized, even when all zones are open, this will happen anyway due to boiler flow requirements being higher than the system needs.
 
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Old 11-13-11, 03:37 PM
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this is a sketch of the system. I did not add in the second zone or the dhw. I can make another one with those if you want. I figured this is fine to show the basic setup. From what I have bene reading I would say it is a p/s system in parallel.

here are the pics. please excuse the quality.

well I have no idea how to post pics. I tried every different way and it won't work. It just shows the [IMG]www.hhhh[/IMG] thing.


~~~~~~~~~~~~~~~~~~~~~~~~~

The original purpose of p/s was to speed up the heating of boiler water and to keep colder water out of the boiler because cold water causes condenstation which is harmful to non condensing boilers. The closely spaced t's allowed a mix of cold return water and hot water from the supply side to circulate through the boiler.

I am wondering if possibly the flow from the return side of the heating circuit is preventing the water from the boiler supply from circulating back into the boiler. ie. that the force of the return water is pushing the supply water and not allowing it down the closely spaced t's. This, I would argue, would prevent the boiler from heating the water as it is outmatched by the amount of cold water in the system.

that or it could jsut be a by product of modulation...the heat system is working well with the outside-reset + thermostat system. I am just nervous to see if the boiler will be able to have a higher temp when the outdoor temp falls.
 
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Old 11-13-11, 04:14 PM
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If you are trying to use tinypic dot com ... forget it... won't work here.

Sign up for a FREE account at Image hosting, free photo sharing & video sharing at Photobucket and upload your pics there. Come back here and drop a link to your PUBLIC album.
 
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Old 11-13-11, 04:43 PM
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boiler pictures by 50benlamond - Photobucket

includes a diagram and several pics.

~~~~~~~~~~~~~~~~~~~~~~~~~

The original purpose of p/s was to speed up the heating of boiler water and to keep colder water out of the boiler because cold water causes condenstation which is harmful to non condensing boilers. The closely spaced t's allowed a mix of cold return water and hot water from the supply side to circulate through the boiler.

I am wondering if possibly the flow from the return side of the heating circuit is preventing the water from the boiler supply from circulating back into the boiler. ie. that the force of the return water is pushing the supply water and not allowing it down the closely spaced t's. This, I would argue, would prevent the boiler from heating the water as it is outmatched by the amount of cold water in the system.

that or it could jsut be a by product of modulation...the heat system is working well with the outside-reset + thermostat system. I am just nervous to see if the boiler will be able to have a higher temp when the outdoor temp falls.
 
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Old 11-13-11, 07:11 PM
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p/s creates hydraulic seperation so the flow of one pump does not affect the flow of another pump. The flow backwards between the tees is dependent on more flow required through the boiler and less flow in the system.
To achieve hydraulic seperation you need the proper distances. It looks like the tees are too far apart and the distance from the tees to the elbows are too close. If the distances are not correct you loose hydraulic seperation.
See this link for more info.
http://www.comfort-calc.net/primary-..._tutorial.html
See drawing #6
 
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Old 11-13-11, 08:10 PM
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The top is what I think the diagram in the link you showed me says. My system is piped as drawn in the bottom pic.
 
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Old 11-15-11, 08:07 PM
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What would you think about piping the manifold so the end of the feed side feeds back into the return side? That would allow non-used feed water to return through the return side allowing warmer water back into the boiler.
 
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Old 11-15-11, 08:26 PM
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In pic # 20 it looks like you have a circ on the feed and one on the return. Is that correct?

I can barely see but the tees for supply and return are indeed next to each other correct?

[IMG][/IMG]

Mike NJ
 
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Old 11-15-11, 08:53 PM
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In this pic you can see the supply and return at the boiler. The line with the black pump is the return.



Here again is a view from a different angle.



In this pic you can see where the closely spaced t-fittings are. You can clearly see the closely spaced-t for the return side...If you follow the supply line you can can guess where the supply closely spaced T is. It's right around where the support strap for the expansion tank is.

Yes, there are two pumps. The one pump is the black one for the boiler return, the other pump pushes the supply water to the manifold. I would say the t-fittings are not more than a foot apart.



best pic. you can see the supply and return close T's.
 

Last edited by silky30; 11-15-11 at 09:23 PM.
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Old 11-15-11, 09:24 PM
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Well I guess one issue is no flo control on the indirect HWH line??? I think I read that in one of your posts. The pumps dont have built in checks right? Thats just a Y strainer in line with the indirect?

I guess I will read your previous posts to update myself. I am not a pro in this area and others here have better knowledge them myself. I only point out what I seen so far.

Looks kind of messed up. Possibly you can take better pics.

The weil mclain site has good piping diagrams for thier ultra boiler. Possibly you can look over that documentation.

Mike NJ
 
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Old 11-15-11, 10:05 PM
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The indirect water heater pump does have a check valve. The taco 0010-1ifc has a built in check valve. Both of the "green" pumps are the same with the internal check valves. There is no check valve on the boiler return line though.

I can try to get better pics but it's hard because it is tight in there. The boiler seems to be installed properly as per the Slant-fin manual, other than no check valve on the return side. But that would just stop water flow when the pumps are off, correct?

I am wondering if I should put a balancing valve on the heating circuit return to limit the amount of water going through that circuit.
 
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Old 11-16-11, 08:30 AM
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Hello,
It's beyond my ability see into that maze and understand what is going on and in what direction. Sorry. Others here may have more talent/experience for that, than i do. The back lighting doesn't help either.
Perhaps you could work on a fully detailed drawing of what is what and the flow directions.

Peter
 
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Old 11-16-11, 11:39 AM
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Old 11-16-11, 01:49 PM
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Originally Posted by silky30 View Post
What would you think about piping the manifold so the end of the feed side feeds back into the return side? That would allow non-used feed water to return through the return side allowing warmer water back into the boiler.
Hello,
Seems like things are confused.
First way back you wanted cooler return temps, to ensure condensing.
Now you want to by-pass the radiators, which will result in increased return temps.

The temperature of the supply water from the boiler can be 130 or 200 and the exact same amount of btu's will be delivered to the house - this is flow rate depedent.
No need to worry about how hot the water is leaving the boiler.
For example: 160,000 btu's are produced by the boiler and the heat load is 160,000
At a flow rate of 25 gallons a minute, a supply temperature of 140*will deliver 160000 btu's to a like load and the return temperature will be 125 degrees
Just because the supply is not 190 degrees does not mean the full amount of heat is not being delivered.

If anything as Mr. Beck noted, the boiler may be too big.
Was there a heat loss done for the house?
200,000 input btu's is a monster boiler, is your house huge and uninsulated?

Peter
 
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Old 11-16-11, 02:28 PM
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The Mod Con

Is it just me? It looks like the manifolds are kinda small for the ammount of water to be going through them. They look like domestic water manifolds.
Sid
 
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Old 11-16-11, 07:44 PM
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I never wanted cooler temperatures. I did want it to maintain condensing temps though! If I open all valves and have full flow the boiler will heat to like 120* Now I don't know if this is because it is modulating down the BTU's because it is not cold out...btu can go from 50,000-200,000. @122* to return temp is about 101-103 so it is maintaining decent delta-T. I don't care if it makes 180* it was just that it went from making 180* to makeign 130 after the modifications i described.

And yes, it is a big house. It is probably a little more than 5500 sqft and was built in 1935 so it is not the most insulated place. Althought the basement has been completely renovated and insulatted. In the main zone there are 23 rads. In the secondary zone there are 7 rads.

I must say again that there is no problem with heating the house. With the outside reset + thermostat the temperature stays between 1-2* of the set temp. Again what I percieve to be a problem could simply be the normal product of modulation!

Well the installed did leave check valves off....
 
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Old 11-17-11, 04:49 AM
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When is a Problem not a Problem?

Don't worry be happy.
Be double happy you have natural gas.
Be tripple happy thinking how much $$$ you are saving vs someone like me, that can't have a mod-con and natural gas, and pays for oil.

Until it gets down to -xx, of course the outdoor reset is modulating down.

Peter
 
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Old 11-17-11, 02:38 PM
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Your boiler controls should tell you what the set point is and if it modulating down. Have you looked at this data to determine if it is performing correctly?
 
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Old 11-18-11, 12:45 AM
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The default display is the actual supply temperature. You can scroll throught several other options. You can see the max temp you set, the max temp for DHW, Actual supply temp, actual return temp, outside temp., and flue gas temp.

It doesn't tell you anywhere if it is modulating down.

If I cycle through boiler options there is a flame sensor read out in miliamps. The boiler runs at 5.4-5.6 milliamps but I don't know if that has an impact on modulation. I knwo it is used as a flame detection sensor to cut the gas supply of ignition fails.
 

Last edited by silky30; 11-18-11 at 01:29 AM.
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Old 11-18-11, 06:06 AM
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I would want the piping as illustrated. It shows 4 check valves total.

It shows the two flow checks as you stated and you are missing one? Your zoned with circs correct?

Page 27 here.

http://www.slantfin.com/images/stori...bcat_ba_40.pdf

Page 37 shows the info on firing rate vs blower speed. Your unit only has HI/LO. You can simply clock your gas meter I believe.

I would not get nutsy with changing any default settings though. You can really mess things up if your not sure what your doing in regards to tweaking.

Has the burner/heat exchanger been serviced? These units need yearly inspection and cleaning of the heat exchangers. It can cause efficiency issues.

Mike NJ
 

Last edited by NJT; 11-18-11 at 04:23 PM.
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Old 11-18-11, 06:36 AM
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so if I understand this correctly. I find out what the specific btu capability of our local natural gas is. Then I run the 20 minute high-load test and measure the m3 of gas used in 3 minutes, multiply that by heating value of gas, then multiply it again by 20?
then i repeat the process while the 20 minute low-load test is on?

There should be a check valve on the boiler circuit, after the circultor pump, before the boiler. There should be 2 more check valves, one after the pump on each heating circuit. Then there should be 1 more on the DHW supply side between the pump and the boiler.

However, I am only missing the check valve that goes between the boiler circulator and the boiler on the heating loops. The 2 heating circuit circulators and the DHW pump have internal flow checks. I don't know what impact the missing check valve would have?

I have noticed two things. The first is that with the DHW on (on priority) and with zone 1 calling for heat, zone 1 does not close down and the pump continues to pump. I am quite sure it is supposed to stop so the DHW heats faster. The second is that when the zones are off there still seems to be flow: say zone 1 calls for heat and zone 2 doesn't. It appears that zone 2 still has some flow through it. I don't think the pump is circulating because the flow meters on the manifold close. The pump does feel like it is vibrating though. Either way, if I close down the return on zone2's manifold the boiler temp will rise. This tells me that there is still flow through zone 2 when it's not calling for it.

No, the burner has not been serviced. It will be though. We have a heating protection and maintenance plan with the gas company so that is up to them! I am sure I can get them to check gas flow etc.

I have everything like fan speed and the important stuf set to default. Stuf like post pump time, fan speed etc. because I don't know what half the stuf does! All I have adjusted is the temps and set the weather compensation.

Again I must say that it could be working perfectly! I mean, if the goal of a modulating boiler is to keep the boiler condensing and a delta-t-20, then it is working perfectly. If the supply temp is 222 the return temp will be like 201-206. The only thing is that there is no way to know if it is modulating. I thought maybe the flame sensor's micro-amps would tell but they never change from 5.5-5.6 and it seems that all that does is sense flame. Could actual fan speed signify modulation? ie. if fuel rate is tied to fan flow, and fan flow is below maximum, could we then conclude it is modulating?


thanks to you and everyone else for the great help!
 
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Old 11-18-11, 02:42 PM
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What are the values for o-d, o-S, and o-t?

What are the values for d-t, b-P, and b-t?
 
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Old 11-18-11, 03:36 PM
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o-d = I believe it is set to 116
o-s = 1.8 I might turn it down. It seems to heat up the house quickly
o-t = is not used because space-heating control mode c-t is set to weather compensation +thermostat. It is blanked out.

d-t is set to storage tank with sensor
b-p is set to the defaul 30 mins
b-t is set to dhw priority
 
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Old 11-18-11, 04:39 PM
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If you look at the graph on page 24, you will se that with the 1.8 slope setting, you will have a supply temperature of 140 degrees when it is roughly 36 degrees outside. Is that about where your outside temperatures have been?
 
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Old 11-18-11, 05:40 PM
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outside temps are a little higher, maybe like 46 or so. However, the house is a 1935 and as far as i know other than being solid brick and plaster there is no insulation on the first and second floords.
 
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Old 11-19-11, 01:49 PM
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starting to think that the weather compensation ramp is too high. I am getting like 7 minute cycles on the thermostat. Every 7 minutes the thermostat clicks which to me is too many cycles per hour.

I am thinking that if I reduce the ramp from 1.8 to 1.4 or so maybe it will take longer to cycle. Either that or I will get rid of the thermostat all together and just run Outdoor Reset,
 
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Old 11-19-11, 02:12 PM
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What is the value for c-t? Is it 0, 1 or 3? It shouldn't be blanked out, I think.

Do you have an outdoor sensor, and if so, where on the building is it? North side?

o-t is the reset curve starting point.

for dhw:
d-t should be 1
b-t can be 0 or 2, depending on what you prefer. If 2, then
b-P can be from 20-80, with default 30 (which should be fine)
 
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Old 11-20-11, 07:15 AM
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C-T is 1 which is outdoor sensor with thermostat. It is not blanked out. When you select option 1 in C-T it blanks out O-T "weather compensation set point". I assume this is the on/off point for the boiler. ie above if temp is above set point the boiler doesn't run.

The outdoor sensor is on the north side.

DHW
D-T= I forget I think it is set as storage tank with sensor because there is an aquastat. Ofcourse I don't think the aquastat is installed correctly, it is on the return side of the boiler loop which never reaches the temperature it's set to.

B-T= is set to 0 DHW priority no time limit.
B-P= the default 30.

How would you know if the boiler is actually modulating? There is not display on this boiler that says if it is or not? Would fan speed indicate modulation?

I watched the boiler running the other day. It started at like ~120, quickly climbed to 140 then slowed down. From there it took about 10 minutes to climb to 146. I checked the fan speed and it said 480..which is the maximum. Would that mean it is not modulating and running at full blast but is incapable of heating the water?

I still have to say that it is maintaining a good delta-T of about 20* and the flu gas never gets above 135. Furthermore you can really hear the condensate dripping into the drain.
 
  #37  
Old 11-21-11, 07:27 AM
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Now I am even more confused. I read through the manual and it says that the boiler-circuit piping should be 1"..the same diameter that that comes from the boiler. The pipe from the boiler up to the closely spaced T's is 1". The piping after that, from the closely spaced T to the circulator pumpe and the closely spaced T to the return manifold is bigger than 1".

I wonder if this is affecting things.
 
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