Boiler flow problem

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  #1  
Old 12-01-08, 05:57 PM
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Boiler flow problem

I have an old system in the house (1938) single pipe system with diverter tee's the old cast iron type main line is 1" reduces to 1/2" on the risers to the rads. when I purchased the house in 91 I replaced the boiler w/a raypack copper boiler I also replaced the rads with copper baseboard. everything worked fine. last year the boiler started leaking, I replaced with the same unit, I also replaced the spirovent. now I cant seem to get hot water into the baseboards I,ve bled and bled, and only been able to get 1 to flow, thought the problem might be the pump so I replaced the little taco it came with with a B&G 100, but still no go. the main line heats fine, but I cant get hot water to flow up into the baseboards any ideas out there?
 
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Old 12-01-08, 06:06 PM
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What is the system pressure at? Ideally you should have 12-15 psi in the system.
 
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Old 12-01-08, 06:32 PM
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system pressure is at 14# constant
 
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Old 12-01-08, 06:45 PM
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Monoflow systems typically have higher head requirements than other piping schemes. The B&G 100 is a low-head circulator, so there's not enough 'oomph' to get the water into the emitter loops.

As I recall, the Raypak is also a fairly high-head boiler. So you are working against both the high-head boiler and the high-head piping.

I'll also guess that you are not pumping away from the expansion tank (e.g., circulator is on the return, expansion tank is on the supply hanging from the spirovent). That doesn't help, either.

First thing I'd do is figure out what circulator is actually required. Figuring head loss in an old monoflow system isn't ridiculously hard, but not as simple as a series loop or other piping scheme. You also need to consult the Raypak manual and see what the flow requirements are so you don't kill the boiler by underpumping, and take account of the head loss in figuring the right circulator for the job. Second thing I'd do is repipe to pumping away.

On the first point, in a small system, you might be able to just throw a Grundfos 15-58 or a Taco 00-R 3-speed circulator in there, and see which speed works best. But I'd absolutely do the pumping away change too.
 
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Old 12-01-08, 07:07 PM
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yea that makes sense, and your right about the expansion tank, problem is, with the old cast iron pipeing and how the boiler is installed its almost impossible to repipe without doing some major work. what problems do I have if I pick a pump with too high a head? Once I reach a high enough head it should start moving the water right? if its too high it shouldn't hurt me!
 
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Old 12-01-08, 07:35 PM
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Too high can be bad:

- too much velocity can erode piping
- too much velocity is noisy
- too much velocity reduces the temperature drop of the circuit (inefficient)
- too much velocity can lead to inefficient, short-cycling boiler (inadequate temperature drop)
- high-head circulators are electricity hogs

Like Goldilocks, you want the one that is 'just right'.

One of the 3-speed circs suggested gives you three shots at choosing the right speed by flipping a switch rather than trying 3 different circs. Flying blind, however, is almost never a good thing. You should at least read up on the boiler's flow requirements, lest it succumb to an early demise (maybe the fate of the last one??)

You can also move the expansion tank connection point to the inlet side of the circulator. Often that merely requires cutting in a tee before the circulator, and piping the tank to that.

But double-check the Raypak manual on how they want their boiler piped and pumped.
 
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Old 12-01-08, 08:04 PM
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gotcha, read up on the raypack the manual said max head 8.0 max flow 5.3 it also indicates that if the overall flow is inadequate then a secondary pump should be installed. but not sure where the best place to install that would be? I will however pickup one of those 3 speed pumps and give it a try. on the other issue, its not so much moving the tank, as it is moving the spirovent, if I move the tank. can I leave the spirovent on the supply? my problem is the return comes back to the boiler right under the support columns for the fireplace upstairs, just isnt room for it on the return side, the tank I can tee in anywhere as long as its piped before the pump, right? it doesn't need to be at a high point.
 
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Old 12-01-08, 08:34 PM
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Sure, leave the spirovent. They work better on the supply when the water is hottest.

Tee for the tank wherever it's convenient. The tank can be placed somewhere else and a 1/2" pipe run to it. Several feet doesn't matter. (I know of someone who's used a stainless braided dishwasher hose and put the expansion tank on the floor in an old wok ring... but he's a professional.)

BUT, if Raypak suggests a secondary circulator, that would probably be the preferred solution. That would even trump moving the expansion tank so you're pumping away (it's a pumping away day here on DIY -- see some other threads...). But there's no reason not to set up the secondary circulator on the supply side so it's pumping away from the existing expansion tank. (Assuming here that they will allow pumping in series and by 'secondary' they don't mean that you have to pipe the whole system as primary/secondary. Exactly what model boiler is this, anyway?)

The most important thing here is to follow the boiler manufacturer specs. The Raypak, as I interpret the manual (keeping in mind I've never seen a Raypak in person), is a rather different boiler from a plain vanilla hunk of cast iron. They go to great lengths to specify flow rates, and provide a piping/pumping setup that makes the thing work right, and safely.
 
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Old 12-01-08, 09:10 PM
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it's a 0066b little guy. it's really secondary heat, old house been added on to a number of times, so I installed additional vents to an existing hvac system to heat and cool the whole place except for 2 rooms at the far end of the house. I still have baseboard in a lot of the other rooms, but as I said its really secondary to those locations. according to the raypack manual it states when the total system head exceeds the available head pressures, a primary/secondary pumping system is recomended. So I'm guessing thats not a secondary pump, but will entail something much more involved? again it seems to work fine as is. water flows thru the main 1" piping back to the boiler. do not have noise problems, no groaning or popping or sound of rushing water, Just can't seem to get it to flow up into the radiators, perplexing thing is, it used to, the B&G 100 thats on this boiler I installed on the old boiler (same model) 6 or 7 years ago when the original pump failed, I did have a little flow problem back then, had to Bleed the baseboard boards both running and off, but after a few days they started flowing and all was fine. couple of years later the tubes in the boiler calcified. had to disassemble the boiler and clean them out, as per raypacks instructions, worked fine for a few more years, then it began to leak, probably a seal, since the unit was 16 years old at that point, and since I'm in a related business(i can buy these things at wholesale ) I just replaced it. according to raypacks website it doesn't appear the operating characteristics have changed over the years, but I just can't get this one to flow into the rads, making me crazy. probably gave you too much info too? sorry
 
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Old 12-01-08, 11:14 PM
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This might not be the solution but try raising the system pressure to around 18-20 psi and see if the rads will heat up. I'm just curious to see if this pressure increase might overcome your flow issues. Who knows, if the pressure gauge is inaccurate the 14 psi reading may actually be lower.
 
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Old 12-02-08, 07:20 AM
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I agree. As a quick check, see if bumping up the pressure 2-3 psi will help. If it does, end of story.

If not....

You are right about the primary/secondary, and yes, that would be a substantial amount of work. Figure 16 on page 17 of the manual shows the boiler piped with closely spaced tees and circulators on the heating zones.

However, I re-read the manual and changed some of my thinking. Here's the manual I read:

http://www.raypak.com/uploads/2100.50AA.pdf

Your system should be piped like Figure 15 on page 17.

That shows a 'pumping away' setup, because the expansion tank is attached to the system on the inlet side of the circulator. They are doing this in part to ensure positive pressure through the boiler. That's fine. Nice simple setup they have there.

Table J on page 16 says the total system pressure drop should be <8.5 ft of head. I would venture a guess that in order to flow at an adequate rate to get the water through all the baseboard takeoff sections, the head of this system is more than 8.5 ft. In theory, the B&G-100 has a shut-off head of 8 ft. i.e., if there's more than 8 ft of head resistance, it won't flow at all. But most manufacturers understate pump performance so you probably have what you observe: some flow, but not enough.

Assuming your boiler is piped per manufacturer's instructions, then I think it would be reasonable to try one of the 3-speed circulators and see which speed works best. You should be right around what they call for in Table J for flow rate and head, i.e., it's not like you are trying to double or triple the flow rate through the boiler.

Adding a temperature gauge on either side of the boiler would also allow you to see what the temp drop is during the heating season, and make sure you have adequate flow through the boiler.

BUT, this is definitely where I get nervous about being a total non-expert giving advice over the internet. You should check with a Raypak rep to make sure what you do is acceptable to them.


If you have calcium-rich water, you might consider filtering the water first. Once filled and purged, the system shouldn't require any more water unless you drain for servicing.
 
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Old 12-02-08, 01:57 PM
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Originally Posted by tkvpice View Post
I have an old system in the house (1938) single pipe system with diverter tee's the old cast iron type main line is 1" reduces to 1/2" on the risers to the rads. when I purchased the house in 91 I replaced the boiler w/a raypack copper boiler I also replaced the rads with copper baseboard. everything worked fine. last year the boiler started leaking, I replaced with the same unit...
It seems that you have iron pipe connected to a copper boiler and copper baseboards.

There could be a problem with galvanic corrosion caused by the dissimilar metals.

I don't have experience with copper boilers, but I think any boiler should be expected to last more than 20 years.
Doug
 
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Old 12-02-08, 04:03 PM
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ok raised system pressure to 18 psi two baseboards (furthest from the boiler) began to flow, but incredibly slow, they're both about 8' long after 1 hour they are hot at the inlets and about body temp at the outlets. there are 2 others (closest to the boiler) that are still cold. no flow. tried to bleed them again but got only water. so I think we're on the right track. going forward I will move the tank, and pickup that 3 speed pump hopefully that will get me the rest of the way. do I dare bringing the pressure up any more? dont I run the risk of popping the pressure relief?
 
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