Monoflow system does not heat well
Hello to all
A customer of mine has a monoflow system that is not keeping up with the cold. I've serviced it for 10 years, only maintenance, never needed a repair. This winter, it will not satisfy the thermostat. It's a one pipe system with 1-1/4 main that runs around the perimeter of the basement. Its a one floor house with mostly thin tube rads and a little baseboard. I purged all the rads/baseboard and only get water. Nothing in the system or house has changed. The boiler heats up to 180deg supply temp and shuts off, pump continues to run. All the rads heat up completely, but they seem to not be giving off enough heat. The only way I can get the thermostat to satisfy is if I increase supply temp to 200deg and even then its running most of the day.
Any suggestions?
Comments
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Either the impeller is getting worn (how old is the pump?) or the system is undersized. 200F isn't unreasonable.
Did it keep up with previous cold snaps? I.E. just this week or earlier when it was warmer?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
2 -
Thanks for responding.
The one major point is that I forgot to mention I changed the pump. It had a taco 007 and I put another one in. No improvement. It could not keep up even with more moderate temperatures. They have a sensi thermostat and I can look up the history going back to the end of 2018 and they never had close to this much usage.
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Something changed from before.
- The Monoflo™ system was installed over 40 years ago?
- This is the first year that the system can't keep up?
- Were there any other changes since the previous years when it worked just fine?
- Boiler replaced
- Expansion tank replaced
- Non-boiler relates work done on the home like carpeting that is blocking the bottom intake of the radiators?
- As you mentioned when bleeding the radiators, no air came out… so it is not an air problem.
- Are there any service valves that may have been closed, that were not fully opened when the repairs were completed?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Same type pump as you said. Did the new one have check valves on it and the old one didn't?
Thinking there's a flow restriction somewhere.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
I presume the system was installed over 40 years ago, house was built in the 50's.
First year it cant keep up. Nothing was changed with regard to the boiler or the house at all. Only water from vents and all valves are open.
Not sure if the old pump had a check valve, but the new one does not.
Thanks again.
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Can you measure the temperature difference between supply and return water? That would tell you if there's a flow problem. Since the system is pressurized a high limit of 200° F should be fine.
—
Bburd2 -
Anything change between last year and this one? Might have a bum pump if that was the only change. Or was the pump changed in response to the lack of heat?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
When I had the system at 180deg I did more of my testing. The supply was 180deg and the return was 160deg.
I also measured the run time which was around 4 minutes or so for the unit to cycle back off.
No changes from this year to last.
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I hate to ask this but…are you sure the pump is pumping in the right direction?
Also: a 007 may be a bit too small for a Monoflo system. I’d use at least a 008 or a Grundfos ups15-58 on high speed.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
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Bottom picture is most recent. As you can see the usage is way high.
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Ironman
Definitely don't have to be afraid to ask, we all make mistakes!
Pump is in the right direction, but I can certainty change out the pump if you think it will help. Thanks
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I agree with @Ironman.
I had an issue with my own house LOL.
Had an old boiler with a Monoflo system 1 zone. The system had a Taco 110. When that failed I put in an 007 and it worked fine.
When I sold the house, I put in a new boiler and an indirect used the same 007 but now had (2) 1" zone valves, indirect and heat. I had put in Honeywell zone valves with a Cv of around 5 I think.
Heating load was only 50 K with a 1 1/4 Monoflo loop. Sounded like a low pressure drop to me. On DHW it was ok with the indirect near the boiler.
On heat the 007 just wouldn't do the job the water was real sluggish getting around the main and this was without the indirect calling.
I took the Honeywell's out and put in 1" Taco valve I think the Cv was 7.5 or 8 and that solved the problem. Maybe I could have swapped to a larger circ for less $$$?
1 -
B&G 100? Probably what was there originally.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
Ironman, thanks for the suggestion of a 008.
I know how to read a pump curve but not sure what Head-Feet I need to overcome for monoflow? Or should I be looking at how much GPM I need? Or both? Looking at the pump curve not sure what to do? The system does work well, just not when it gets very cold, so I know I am getting some flow. Leaving out the cost difference, what about a 0010. The pump curve shows nearing the limit of the 007 at 8 Head-Feet I get 8 GPM from the 007, 10 GPM from a 008 and 15 from a 0010. Anything below 7 Head-Feet and the 007 will work better than the 008 but much less than a 0010. Only nearing the max for the 007 at 10 would I need the 008.
What do you think? Thanks.
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Is the pressure in the boiler lower than it has been previously? Would that make any difference? I'm not sure.
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The problem is the baseboard . They were added to the original system incorrectly ….
There was an error rendering this rich post.
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I’ve been maintaining the system for years and it always worked well. I’ve never had to do a repair, just maintenances but never had a complaint.
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Since the job works except in the really cold weather that would seem you are riding the edge of the pump curve,
I would take the boiler output in BTU and divide it by 10,000. That will give you the GPM you need. Then find a pump that will deliver that gpm with a head slightly higher than the pump you now have.
The other way is to calculate the head you need by measuring the total feet of pipe you have + elbows + tees + monoflow tees, boiler resistance, air scoop, valves etc and come up with a head calculation
If you get a circ that is too large you will have noise
1 -
I see a 180° Supply what about Return Temperature?
How caked are the emitters?
Any new carpeting?
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EBEBRATT-Ed thank you for the info !
Pecmsg the return is 160. Emitters are slightly dirty. Didnt seem to me enough to cause a problem. No new carpet. Homeowner says absolutely nothing has changed recently.
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the numbers in late 2021 into 2022 were pretty high over a couple of months on the charts, so is it possible this is just a longer colder spell?
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The head is relatively low in a monoflo loop but you need a fair bit of velocity for the water to take both branches of the diverter tees.
You may need more gpm than @EBEBRATT-Ed calculates to encourage enough flow in the branches. It would be a balance between the max velocity for the pipe size and what it takes to move the output of the boiler but if the boiler is enough smaller than the piping the water might just happily circulate around the run of the monoflo tees if you calculate only on what you need to move the heat.
Are there any balancing valves or bypass valves that need to be partially closed that are now wide open?
Just because you don't get air when you bleed doesn't mean there isn't air somewhere that can't get to the bleeder valves but more bleeding isn't going to fix that if it is the problem.
2 -
slow the flow down shoot for 30-40*
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Can you check the temps in and out of a few basebords? You will probably find the problem their. I would go down the line and check the main temp at the first tee and the first baseboard inlet and then the baseboard outlet and at the Monoflo tee. Repeat this down the line.
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So you're saying to check the inlet and outlet of all rads and baseboard?
What should the difference be ? I can do this all from the basement if I have access ?
Thanks
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Got it. Thanks. If there is air somewhere in the system, how would I get it out ?
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The measuring of the inlet and outlet temp is to get an idea of if there is flow through the emitter and how much. If the inlet is about boiler temp and the outlet is just warm you know there isn't enough flow. 20 f degrees is the textbook example but it would probably work find with 40 as well as long as the supply was around 160-180.
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mattmia2
got it. thanks
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Also to your question about valves, there are only to by the boiler, two standard ball valves, supply and return.
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Is it worth checking the air separator for restriction? I would have to drain the entire boiler. Like I said at the beginning of the post, I've serviced this unit for ten years and its always had a 007 and now it isn't working.
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There will be a air vent on each loop …
There was an error rendering this rich post.
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That's what you want for an air separator. If the emitters are getting at least some flow and that is on the outlet of the boiler the aor should eventually work its way out there. Is the cap loose on it so it can vent or did it start leaking and someone tightened the cap down?
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you mean the small cap? It is tight. I took it off and depressed the pin and only water came out. Is there a screen inside? Could that be clogged?
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If the cap is tight the vent won't work, that is where the air comes out. There is a float and a needle valve in there. If only water came out then there isn't any air in that separator. There is a mesh of sorts in there, not sure if it could clog enough to cause a problem.
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What is the Btu/hr rating of the boiler? If this is a relatively large system, a Taco 007 may be too small to really get the necessary flow rates for the monoflo diverter Tees to perform well. A Taco 0012 (which is an HV pump equivalent) is often a better choice with a monoflo system.
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Its 128,000 in 106,000 out. 1 1/4 supply/return copper pipe.
As I've said they have always had a 007 with no complaints until now, but I'm not opposed to replacing it if that will solve the problem.
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If it worked before, I'd look for restriction or impeller failure. How old is the pump?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
What changed ?
There was an error rendering this rich post.
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Like I posted above I had an oo7 with a monoflow loop in my house and it was ok. Then I changed the boiler and put 2 zone valves in (3.5Cv Honeywell valves) and the 007 would not do the job . Very sluggish moving the water. The indirect was ok because it was near the boiler but even with the indirect valve shut it wouldn't do the monoflow loop which was 1 1/4" copper.
I fixed it by taking out the Honeywell valve on the monoflow loop and putting in a Taco valve that had a Cv of around 8.
just that little bit of added restriction was enough to not make it work
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