Installed a Boiler and Have Questions

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Dana

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A thermostatic mixing valve on the system bypass could do it by returning 100% of the boiler output back to the input until the boiler came up to temp, (as previously discussed) but a HydroStat 3250 and the additional heat-well option would give you a LWCO function as well.

It looks like you get at least ~3 minutes of burn after the entering water temp hits 125F. Judging by the temperature ramp rate of the basement zone, turning the circulator off or a thermostatic mixer bypass during cold starts would cut the heat-up time on the boiler to about 1-2 minutes, which would make some of those burn cycles pretty short. Raising the high limit another 10F would get it reliably above 5 minutes per burn even with those fixes. With the smart economizers it's customary to set the high-limit to something fairly high, and let the controller manage it from there. With a heat purging controller if the boiler is already hot a call for heat from the basement might even be satisfied without the burner firing.
 

Reicherb

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So, I've got the return temp up to 130 in 2-3 minutes with the bypass loop. I sent a message to Weil Mclain to confirm that they agreed that my setup was correct.

They indicated that the boiler temp should be 180-210 and that the return temp should be 160-170 to avoid boiler damage. They went on to say that the output should be tempered if I have a radiant system.

I really don't need to have it that high. Correct?

Thanks for the continued support.
 

Dana

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So, I've got the return temp up to 130 in 2-3 minutes with the bypass loop. I sent a message to Weil Mclain to confirm that they agreed that my setup was correct.

They indicated that the boiler temp should be 180-210 and that the return temp should be 160-170 to avoid boiler damage. They went on to say that the output should be tempered if I have a radiant system.

I really don't need to have it that high. Correct?

Thanks for the continued support.

I'm very surprised that anyone at Weil McLain would assert that it required a 160°-170°F return temp to avoid boiler damage. There are existence proofs of W-M boiler where even the output never hit 160F for decades and still going strong. If that's their assertion, they should be able to explain why that would be true, and detail what type of damage occurs.

But there is no condensation going on inside the boiler (none!) when the entering water temperature at the boiler is 130°F or higher, and chronic condensation would definitely damage the boiler.

On right column on page 16 of the manual under the heading "System water piping" they refer to

See FIGURE 9 (diaphragm-type or bladder-type expansion tank) or FIGURE 10 (closed-type expansion tank), and Table 3 below, for near-boiler and single-zone systems designed for return water of at least 130°F.

And that's just the first reference of about a dozen mentioning an return water of at least 130°F, reinforced by the warning verbiage in the block at the bottom of pages 20, 22, and 24. So why would the person on the phone be calling for return water of at least 160°-170°F when the "magic number" in the manual is all about maintaining a minimum entering water temp of 130°F?

BTW: The system bypass piping approach you are using is shown in Figure 17 on page 25 of the manual.

The business about tempering the output water for radiant systems also seems too un-nuanced. A lot depends on the type of radiant floor/ceiling. An entering water temp of 180F water is just fine in suspended tube radiant floors and some types of staple-ups, but would be problematic in radiant slabs.
 

Reicherb

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I asked her to confirm it and she did...

Regardless, I've had to put the water up to 170 to keep the return over 130. Below is a picture of my setup with the valves adjusted to ensure balanced flow and enough bypass.

Here are the temps I'm seeing. High limit is 170. Low limit is 150.
Outside air temp is only 36. Only indicates there isn't much call for heat.

Minute Return Temp Boiler Temp Boiler Status Zone Status
0 70 70 Boiler On, Pump On All 3 zones calling for heat
1 75 80 Boiler On, Pump On All 3 zones calling for heat
2 95 105 Boiler On, Pump On All 3 zones calling for heat
3 115 130 Boiler On, Pump On All 3 zones calling for heat
4 135 150 Boiler On, Pump On All 3 zones calling for heat
5 155 165 Boiler On, Pump On All 3 zones calling for heat
6 165 170 Boiler Off, Pump On All 3 zones calling for heat
7 160 160 Boiler Off, Pump On All 3 zones calling for heat
8 150 150 Boiler Off, Pump On All 3 zones calling for heat
9 140 145 Boiler On, Pump On All 3 zones calling for heat
10 145 160 Boiler On, Pump On All 3 zones calling for heat
11 160 170 Boiler Off, Pump On All 3 zones calling for heat
12 160 170 Boiler Off, Pump On All 3 zones calling for heat
13 155 155 Boiler Off, Pump On All 3 zones calling for heat
14 145 145 Boiler On, Pump On All 3 zones calling for heat
15 140 150 Boiler On, Pump On All 3 zones calling for heat
16 155 165 Boiler On, Pump On All 3 zones calling for heat
17 165 170 Boiler Off, Pump On All 3 zones calling for heat
18 160 165 Boiler Off, Pump On All 3 zones calling for heat
19 150 150 Boiler Off, Pump On All 3 zones calling for heat
20 140 145 Boiler On, Pump On All 3 zones calling for heat
21 145 155 Boiler On, Pump On All 3 zones calling for heat
22 160 170 Boiler Off, Pump On All 3 zones calling for heat
23 165 170 Boiler Off, Pump On All 3 zones calling for heat
24 155 160 Boiler Off, Pump On All 3 zones calling for heat
25 145 150 Boiler On, Pump On All 3 zones calling for heat
26 140 145 Boiler On, Pump On All 3 zones calling for heat
27 150 160 Boiler On, Pump On All 3 zones calling for heat
28 165 175 Boiler Off, Pump On All 3 zones calling for heat
29 160 165 Boiler Off, Pump On All 3 zones calling for heat
30 155 155 Boiler Off, Pump On All 3 zones calling for heat
31 145 150 Boiler On, Pump On All 3 zones calling for heat
32 145 150 Boiler On, Pump On All 3 zones calling for heat
33 155 165 Boiler On, Pump On All 3 zones calling for heat
34 165 170 Boiler Off, Pump On All 3 zones calling for heat
35 160 165 Boiler Off, Pump On All 3 zones calling for heat

I could probably go down to 165 but worry that when it's actually cold, the return will be lower.

I assume this is short cycle conditions but that when it's actually cold, the cycle will be longer.

What do you think about all of this. Am I finally in a good place?

Thanks for all of your help.
 

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Dana

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I'm not worried about the time it takes to get the return water above 130F.

If it's hitting the high limit with all three zones continuously calling for heat, raise the high limit. You lose more efficiency with the 3 minutes on/3 minutes off cycling than you would lose in distribution losses by setting the high limit to 190F-200F (or whatever it takes.) That cycling on continuous calls for heat from all zones won't change with outdoor temperature.

A high limit of 170F is only 20F above the 150F low limit. If it's possible to set the differential wider than 20F it will lengthen the cycles, but raising the high limit also lengthens the cycles due to a greater fraction of the heat input being emitted in the zones rather than causing the water temperature faster.

If you can get it up to at least 5 minute burns during continuous 3-zone calls for heat tweaking the high-limit & low limit settings it'll be fine.

The way it's currently set up delivering a ~50% duty cycle on burner the average heat rate going into the house is only half the boiler's output, so you'll probably need to run a higher high-limit to keep up with the load when it's actually cold out.
 

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If I can lower the low limit and the return dips a bit below 130 before the boiler fires, that's ok?

Thanks
 

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If I can lower the low limit and the return dips a bit below 130 before the boiler fires, that's ok?

Thanks

As long as it doesn't hit 125F it's still pretty safe. It looks like with the low limit set to 150F the EWT drops to 140F by the time it re-fires, so if you set the low limit to 140F it'll probably refire at a safe EWT of 130F.

BTW: In the statement, "I asked her to confirm it and she did...", what is the "...it..." that got confirmed? (Alleged damage to the boiler at EWTs under 160F? An EWT of 130F being OK, per the manual?)
 

Reicherb

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Here is the discussion I had with Weil McLain
Me:
I recently installed a Weil Mclain CGA-25 Boiler. The return temperature is low when the boiler comes on after a long period of no calls for heat. I added a bypass loop to divert some of the boiler output back to the boiler input to help reduce the time it take for the return temperature to reach 130 degrees. It's currently taking about 5 minutes. Will that cause damage to the boiler? If so can you advise a system that would prevent this?

WM:
Yes, the CGA is a cast iron boiler so it can’t take low water temperatures. If you don’t raise the water temperatures up to at least 160170 it will damage the boiler. Condensation will occur on the inside cast iron. Weil-McLain recommends the high limit be set to a minimum of 180 and can go as high as 210.

Me:
I’ve been able to adjust the ball valves and have the return temperature up to 130 within 3 minutes with the high limit set to 155. Is this ok? This is only when starting after the system has been in unoccupied setback. Once the loops are up to temp, the return is 130 when the output is 155.

WM:
Too low – Min of 180 as high as 210. If you have radiant then the water needs to be tempered to and from that system.



I'm going to work on the low limit. There isn't such an adjustment. There is an "economizer" dial which I assume effectively is the low limit.
 

Reicherb

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So the economizer reads like it's going to adjust the low limit but as far as I can tell, it does nothing...

I left the high limit at 170 which puts the low limit at 150. I opened the valve supplying the zones a bit in hopes of getting a longer burn. I got up to 3 minutes consistently. The trade off is that the initial warm up takes longer. the reading are below.

Did I go too far? Do I need to get it up to temp sooner?

Is the initial warm ok and I should go a bit further in hopes of getting longer burns?

Should I lower the high limit to 165 since the return never drops below 140?

Minute Return Temp Boiler Temp Boiler Status Zone Status
0 70 70 On All 3 Calling
1 75 85 On All 3 Calling
2 90 100 On All 3 Calling
3 105 115 On All 3 Calling
4 110 120 On All 3 Calling
5 115 130 On All 3 Calling
6 120 130 On All 3 Calling
7 125 135 On All 3 Calling
8 125 140 On All 3 Calling
9 130 140 On All 3 Calling
10 130 140 On All 3 Calling
11 130 140 On All 3 Calling
12 135 145 On All 3 Calling
13 135 145 On All 3 Calling
14 140 150 On All 3 Calling
15 145 155 On All 3 Calling
16 150 160 On All 3 Calling
17 155 165 On All 3 Calling
18 155 165 On All 3 Calling
19 160 170 Pump Only All 3 Calling
20 155 160 Pump Only All 3 Calling
21 145 145 On All 3 Calling
22 140 145 On All 3 Calling
23 145 155 On All 3 Calling
24 155 165 On All 3 Calling
25 160 170 Pump Only All 3 Calling
26 155 160 Pump Only All 3 Calling
27 145 145 On All 3 Calling
28 140 150 On All 3 Calling
29 150 160 On All 3 Calling
30 160 170 Pump Only All 3 Calling
31 155 160 Pump Only All 3 Calling
32 150 150 Pump Only All 3 Calling
33 140 145 On All 3 Calling
34 145 155 On All 3 Calling
35 155 170 On All 3 Calling
36 160 170 Pump Only All 3 Calling
37 155 155 Pump Only All 3 Calling
38 140 145 On All 3 Calling
39 145 150 On All 3 Calling
40 155 165 On All 3 Calling
41 160 170 Pump Only All 3 Calling
42 155 160 Pump Only All 3 Calling
43 145 150 On All 3 Calling
44 140 145 On All 3 Calling
45 150 160 On All 3 Calling
46 160 170 Pump Only All 3 Calling
47 160 165 Pump Only All 3 Calling
48 150 155 Pump Only All 3 Calling
49 140 145 On All 3 Calling
50 145 150 On All 3 Calling
51 155 165 On All 3 Calling
52 160 170 Pump Only All 3 Calling
53 155 160 Pump Only All 3 Calling
54 145 145 On All 3 Calling
55 140 150 On All 3 Calling

Thanks again for all of your help. It's greatly appreciate.

FWIW: I haven't compared degree days but my gas consumption is down the last 2 months compared to last year.
 

Dana

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Looks like you're getting 3-4 minute burns out of it with the high limit set to only 170F, a modest improvement at best.

Don't be timid- crank it to 190F or 200F, see if you can't get at least a higher duty cycle and longer burns out of it with all 3 zone calling. You can always back down.

Read up in the manual on how the economizer is supposed to be set up (and it's theory of operation.) I don't recall older CGa boilers having any controls labeled "economizer".
 

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Should I be worried about the time it takes to get up to temperature after setback?

I'll crank it up tomorrow and report back.

Attached is a picture of the economizer info.
 

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Dana

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Don't sweat the time it takes to get up to temp from a cold start or deep setback. If it can't tolerate that they wouldn't design it to be cold-started. The key factor is that the vast majority of the burn time the entering water temp will be well above 130F.

The economizer is a fairly dumb heat purging control, that would improve the as-used efficiency if the boiler was significantly oversized. The reason it doesn't seem to have much affect is that it's (almost) never the case that "... the available hot water will satisfy the demand..." at the tempertures you're running, though occasionally might have enough heat to cover the immediate needs of a single zone calling for heat if a recent call for heat had parked the boiler at 180F or higher. With the high limit set to 160F that would pretty much never happen- there simply isn't very much thermal mass in the CGa-25, and the controller probably won't attempt to pre-purge heat from a already at 150-160F, since it has to re-fire before it drops to 140F to avoid a slug of sub-130F water. You may notice it actually doing something with the high-limit set to 180-200F.
 

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I turned the high limit up to 190 and got 4 minute burns with a low return of 160 after the boiler was up to temperature.
I turned the high limit up to 200 and got 5.5 minute burns with a low return of 165 after the boiler was up to temperature.

Should I stick with 200?

If the time to get up to temp doesn't mater, should I adjust the bypass flow to get the return closer to 130? That should also increase the burn time. It took about 10 minutes for both of the above scenarios. I might be able to lower the high limit a bit, adjust the bypass flow, and still keep the burn time over 5 minutes and the return over 130.

At around 180, the boiler popped a couple of times from expansion/contraction. That's no concern. Correct?

Thanks.
 

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Go ahead and leave the high-limit at 200F, turn the economizer to MAX, see how it behaves on zone calls when only 1 or two zones are calling for heat. A data-logger that just tracks the burner times is good enough- no need to rigorously run experiments here. If it's only a handful of burns per hour, with average burn times in the 5 minute range or higher you're good to go.

It might be interesting to test the economizer by running the boiler fully up to temp, wait 10 minutes than turn up just one of the zone thermostats, to see how much pre-purge time it delivers, and the boiler temperature at which it fires up.

Most cast iron boilers can take a delta-T of no more than 50F, some only 40F (there's probably a spec for the max delta-T in the CGa manual somewhere- I'd have to look it up) so by no means should the bypass be tweaked to deliver 130F when the output water is hotter than 170F.

If the boiler had never seen 180F or higher before there might have some creaking going on as the through-bolts holding the heat exchanger plates together stretch and move a bit settling in to their newer wider operating temperature range. As long as the delta-T was within spec when the pops were happening it probably doesn't signify anything, and may stop happening after a few dozen thermal cycles.
 

Reicherb

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I can't get the economizer to do anything. I did as you suggested and the boiler fires at 179.

I let everything warm up and then ran as normal for a while. Here is what I logged. Anything of concern here?

Minute, Return Temp, Boiler Temp, Boiler Status, Zones Calling
0 180 180 Circ Pump On Basement
1 175 180 On Basement
2 170 180 On Basement
3 175 190 On Basement and 1st Floor
4 180 190 On Basement and 1st Floor
5 180 195 On 1st Floor
6 190 200 Circ Pump On 1st Floor
7 175 195 Off None
8 170 195 Off None
9 170 195 Off None
10 170 195 Off None
11 170 190 Off None
12 170 190 Off None
13 170 185 Off None
14 170 185 Off None
15 170 185 Off None
16 170 175 On 1st Floor
17 160 165 On 1st Floor
18 165 175 On 1st Floor
19 170 180 On 1st Floor
20 175 190 Off None
21 170 200 Off None
22 175 200 Off None
23 180 200 Off None
24 180 200 Off None
25 175 180 Circ Pump On 2nd Floor
26 160 160 On 2nd Floor
27 160 170 On 2nd Floor
28 150 185 Off None
29 160 190 Off None
30 165 190 Off None
31 165 190 Off None
32 170 180 On Basement
33 165 170 On Basement
34 165 175 On Basement
35 175 185 On Basement
36 180 190 On Basement
37 185 200 Off None
38 190 200 Circ Pump On 1st Floor
39 180 180 Circ Pump On 1st Floor
40 160 165 On 1st Floor
41 165 175 Off None
42 155 190 Off None
43 160 190 Off None
44 165 190 Off None
45 170 190 Off None
46 170 185 Off None
47 170 185 Off None
48 165 180 Off None
49 170 175 On Basement
50 165 170 On Basement
51 170 180 On Basement
52 180 190 On Basement
53 180 200 Off None
54 180 200 Off None
55 185 200 Off None
56 190 200 Off None
57 190 200 Off None
58 190 200 Off None
59 190 200 Off None
60 190 200 Off None
61 190 200 Off None
62 185 200 Off None
63 185 200 Off None
64 185 195 Off None
65 175 180 On Basement
66 170 175 On Basement
67 170 180 On Basement
68 175 185 On 1st Floor
69 180 190 On 1st Floor
70 180 195 On 1st Floor
71 180 195 On 1st Floor
72 180 200 Off Off
73 175 200 Off Off
74 180 200 Off Off
75 185 200 Off Off
76 185 200 Off Off
77 185 200 Off Off
78 185 200 Off Off
79 180 195 Off Off
80 180 195 Off Off
81 170 175 On Basement
82 170 175 On Basement
83 175 175 On Basement
84 175 175 Off Off
85 175 200 Off Off
86 180 200 Off Off
87 185 200 Off Off
88 185 200 Off Off
89 185 200 Off Off
90 185 200 Off Off
91 185 200 Off Off
92 180 195 Off Off
93 180 195 Off Off
94 180 195 Off Off
95 180 195 Off Off
96 180 185 Off Off
97 160 160 On 2nd Floor
98 150 155 On 2nd Floor
99 150 160 On Basement
100 160 175 On Basement
101 175 190 On Basement
102 175 200 Off Off
103 180 200 Off Off
104 180 200 Off Off
105 185 200 Off Off
106 185 200 Off Off
107 185 200 Off Off
108 185 200 Off Off
109 180 195 Off Off
110 180 195 Off Off
 

Dana

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Looks fine. While there may be a few 3-minute burns thrown in when only a single zone calls for heat, the overall average is north of 4 minutes. In normal operation you can expect overlapping calls for from multiple zones a lot of the time.

The peak delta-T across the boiler was 35F (at minute 42) which occurred when no pumping was going on, and if it the temperature was taken external to the boiler at no-flow it's not reflecting the temperature delta inside the boiler itself. The fact that the low-temp rose by 5F in the following minute still with no flow and no pumping tells me that the boiler's temperature on return side was actually warmer than the 155F indicated. During normal pumped operation the delta-Ts were usually between 10-15F, (sometimes 0-5F on the basement zone-only) which is fine.

I'm not too surprised that the dumbed-down version of a heat purge controller doesn't really do much. It probably did just barely enough in some test configuration to make it the boiler compliant with current regulations, but in practice it's not nearly as useful as some of the more sophisticated digital heat purge controllers.
 
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