One zone of FHW system is only luke-warm

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  #1  
Old 11-20-14, 08:04 AM
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One zone of FHW system is only luke-warm

I recently bought a house that has a Weil-McLain #2 oil boiler with 4 zones. The unit is 5 years old. One zone feeds a hot water tank, one feeds the basement (and the thermostat is always off), one feeds a living area, and one feeds two bedrooms. Each bedroom has about 6 feet of baseboard (which seems small) and the total area of the rooms is maybe 400 sqft.

This bedroom zone gets some heat, but barely.... the thermostat could be set at 70 all day and the room doesn't get hotter than 61. The baseboards do get warm, so it is sort of working, but it's often only luke-warm, not the hotter temp felt in the other zones. But sometimes it does feel as hot as it should. Even over night when all other zones are essentially off, this the bedroom temp didn't get about 61 (when the thermostat is set on 70 all night).

I do not hear any pinging or popping within the pipes that indicate air in the system. All of the other zones work fine.

I've changed thermostats in the room and the problem remains. The circulation pump is a Grundfos UPS15-58FC with 3 speeds, and the dial is set to medium.

What could be causing the issue? Are there any basics I can check before hiring a plumber?

I appreciate any advice. Thanks
 
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  #2  
Old 11-20-14, 08:48 AM
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Tell us the model of the boiler and the BTU output.

Take a look at the temperature and pressure gauge on the boiler and let us know the readings.

There may be a partial air blockage in that one zone.

Can you post some pictures of the installation so we can see what you are working on? Show us all the valves and what not around the boiler. This will help us tell you what valves to open and close to get the air out...

Is 400 square feet accurate? That is a small house, isn't it?
 
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Old 11-21-14, 10:32 AM
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It's actually a Burnham unit, not Weil-McLain. Model number MPO115-TB. I believe it has an 88k BTU output based on what I've read online.

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I've included a picture of the temp and pressure gauge. It reads around 170F and around 15 psi.

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Here are pictures of the installation, etc. The close-up picture of the circulation pump is for the bedroom zone.

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The 400 sqft is for just the two bedrooms that are on the zone - each bedroom is approx. 12'x12' and there's a small bath and two closets. The entire heated area of the house is around 2,000 sqft, about 800 of which is in the basement where the heat is not turned on.

Thanks again for the advice and help.
 

Last edited by NJT; 11-21-14 at 04:26 PM.
  #4  
Old 11-21-14, 04:22 PM
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OK, great...

Before I start with a 'how to', I'd like to mention that sometimes when pumps with internal check valves are installed pumping upward as yours are, it's possible for the pump itself to become air bound. Since a centrifugal pump can't pump air, if the pump is full of air it won't pump and open the check valve. The pump will just 'sit and spin' and do nothing. Information just in case you ever run into the situation.

Turn boiler off and allow to cool to 100F or less.

Connect your drain hose with the end submerged in a bucket or laundry tub so you can see bubbles to the drain valve at the left side of the return manifold in this pic:



Close the ball valve on the return to the boiler.

Close the other two ball valves on the zones you are NOT purging.

Open the drain valve and lift up on the 'fast fill' lever on top of the pressure reducing valve (the water regulator that feeds in above the expansion tank).

When you lift that lever, keep an eye on the boiler pressure gauge and 'modulate' the lever to keep the pressure in the boiler around 25 PSI.

When no more bubbles out the hose, release the fast fill lever and then close the drain.

Open all the valves you closed and restart the system.

This should get all the air out.

I'm surprised you have air at all... your system has all the right stuff, properly piped, etc.
 
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Old 11-21-14, 04:36 PM
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the temp and pressure gauge. It reads around 170F and around 15 psi.
If the gauge is accurate, 15 PSI at 170F may be a bit low... it may be OK though...

If the COLD pressure on the boiler is not less than 12 PSI and your home is two stories (not three), the 15 PSI is fine.

If the cold pressure is less than 12 PSI, you should bump it up a bit.

Each bedroom has about 6 feet of baseboard (which seems small)
Yes it does. Each room about 12X12, 144 square feet, if the heat loss in those rooms is low, let's say 25 BTUH / SQ FT then it means you would need about 3600 BTUH of heat emitters to maintain the temperature.

Six-ish feet of fin tube baseboard would output about 3300 BTUH. (using 550 BTUH per lineal foot).

So, you see there's a bit of a shortfall of emitter output in those rooms.

If your heat loss is a bit more, then the shortfall is that much more.

You could use about 2 more feet of BB in those rooms.

How much BB is in the bath? Is it cold too?

Your outdoor reset module may not be helping matters either if the 'reset curve' isn't set up correctly.

Have you learned about that module yet? Can you tell me what your settings are?
 
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Old 11-21-14, 04:41 PM
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I use a lower number for BTU output of the BB elements than the manufacturer publishes. Real life conditions might even be less than 550.

This is because those numbers are for NEW, perfectly SPOTLESS fin tube installed in the best conditions. i.e. no furniture in front of, no curtains blocking, no wall to wall carpet closing up the bottom air inlet.

If any of these conditions exist, try moving the furniture out a bit, shortening the curtains, trimming the carpeting back, etc.

Even a very thin coat of dust on the BOTTOM of the fins will greatly reduce the heat output.

If the covers have not been off and the fins brushed and vacuumed in a while, it would be worth your while to do so. Might as well maximize what you've got!
 
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Old 11-21-14, 05:41 PM
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NJ Trooper -- many thanks for your help, I greatly appreciate it.

I'll follow your steps for purging the air out of the zone this weekend.

If the COLD pressure on the boiler is not less than 12 PSI and your home is two stories (not three), the 15 PSI is fine.
It is a two-story house, split-level house.

How much BB is in the bath? Is it cold too?
There is no BB in any of the closets or bath. The bath doesn't abut an exterior wall, and the door is always open, so it is the same temp as the bedroom. The closet in one bedroom does abut the exterior wall and it is freezing after the door is shut for an hour. Again, seems odd that there's no BB in a room abutting an exterior wall with a door.

Your outdoor reset module may not be helping matters either if the 'reset curve' isn't set up correctly.

Have you learned about that module yet? Can you tell me what your settings are?
I honestly don't know anything about that module. I'll read about it and post the settings on this thread.

Thanks for the advice on how to maximize the BTU output of the BB. We have no furniture or curtains up against them, but they're definitely not spotless. That'll change this weekend.

Thanks again!
 
  #8  
Old 11-25-14, 10:17 AM
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NJ Trooper -

I followed your steps for removing air from the zone this weekend, and everything seemed to work, but it's now 60 degrees outside so it's hard to tell if the problem is solved. After I removed the air, I shut off all other zones and cranked the problem zone to 72. It got up to 72 in an hour or so, which it hadn't been able to do before, so it seems like things are fixed. I also vacuumed all BB thoroughly.

When removing the air, I didn't really see many bubbles from the hose... Is it possible for only a small amount of air to have caused the problems? (as opposed to a very noticeable amount of bubbles from the hose).

One last question - I should expect a decrease in heat from the baseboard when a bath or shower is being run? Is the boiler capable of outputting hot water and BB heat simultaneously without a decrease to either? I assume not.

Thanks,

Dan
 
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Old 11-25-14, 11:21 AM
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Hi Dan,

Is it possible for only a small amount of air to have caused the problems?
It can... it doesn't take a lot of air to cut flow.

I should expect a decrease in heat from the baseboard when a bath or shower is being run? Is the boiler capable of outputting hot water and BB heat simultaneously without a decrease to either?
You've got what's called an 'indirect water heater'. This means that you've got STORAGE of hot water. The water heater only calls the boiler when the tank needs heat. You boiler is probably big enough to provide both heat to the baseboards and to recharge the tank when it needs it.

Your TACO control panel probably has a switch inside labeled 'PRIORITY'. What this switch does if set to priority is DISABLE the heat to the home while the water heater is recovering.

So, the bottom line is that if set to priority, when the water heater calls for heat, the system will IGNORE heat calls from the home until the tank is up to temperature.

If you do not have priority set, both the heat and hot water can call at the same time. If the boiler is big enough, no problem... if boiler isn't big enough, use priority.

You do need to understand how the OUTDOOR RESET MODULE operates as that has a very direct bearing on the heating patterns of the home. Tell us all the settings of that module and we'll do a 'sanity check' to see if they are all reasonable.
 
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Old 12-01-14, 11:58 AM
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NJ Trooper,

Sorry for the delayed reply. I appreciate the clarification with the control panel settings for priority. It has been cold recently and the system seems to be operating correctly. This morning, two zones increased to the correct temperature in 30 mins with the shower on.

You do need to understand how the OUTDOOR RESET MODULE operates as that has a very direct bearing on the heating patterns of the home. Tell us all the settings of that module and we'll do a 'sanity check' to see if they are all reasonable.
Where would one find the outdoor reset module? Beyond the items in the pictures I've posted previously, I can't locate any module indoors that appears to be an outdoor reset. On the exterior of the house, there is one box (non-phone, non-cable) which has a low voltage wire and a label of CO2 detection, etc. There were no 'settings', only two wires. Perhaps this box acts as an outdoor thermocouple for an indoor module? I will add a photo of this box tonight.

Thanks,

Dan
 
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Old 12-01-14, 12:38 PM
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In front of your pumps are a large green box (your zone control panel) and above that a smaller box with a display and some buttons.

The box on top is the Outdoor Reset control. Looks like a Taco equivalent of the Tekmar 256, I think their model number is PC-700. Is that the model number on it?

CO2 you say? sounds odd that there be something to do with CO2 outdoors... but maybe they just used any old plastic box they had on hand to house the temperature sensor. Does that wire lead back to the module?
 
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Old 12-02-14, 10:44 AM
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NJ Trooper,

I will check out the settings on the outdoor control module tonight and post them. I tried to load the pictures of that outside box, but they're not uploading for some reason. I'll try again soon. Thanks

Dan
 
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Old 12-03-14, 06:21 AM
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NJ Trooper,

The wire from the box outside does appear to lead to the outdoor reset module of the boiler, but I mis-read the CO2 indication -- it actually says "outdoor sensor" with an Os designation. Here's the picture:

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Here are the settings from the outdoor reset module:

- OUTDR (VIEW) 32F
- BOIL (VIEW) 139F
- BOIL (with arrow over "start") 71F
- OUTDR (with arrow over "start") 70F
- BOIL (DSGN) 190F
- OUTDR (DSGN) 10F
- BOIL (MIN) 140F
- DIFF Ad
- WWSD 70F

I have a video of the settings I can upload if that's easier.

As a further update, the heat in the problem zone appears to be much more responsive to the thermostat lately. The temp. increased 5 degrees in 45 minutes with other zones operating and the shower running.

Thanks,

Dan
 
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Old 12-03-14, 03:27 PM
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- OUTDR (VIEW) 32F
- BOIL (VIEW) 139F
- BOIL (with arrow over "start") 71F
- OUTDR (with arrow over "start") 70F
- BOIL (DSGN) 190F
- OUTDR (DSGN) 10F
- BOIL (MIN) 140F
- DIFF Ad
- WWSD 70F
These are pretty 'sane' settings.

The only one that might not be 'correct' is the OUTDR DSGN of +10F.

I suspect that your coldest days may in fact be colder than that. There's tables for finding that value available on the net.

For example:

New Hampshire
Berlin -9
Claremont -4
Concord AP -2
Keene -7
Laconia -5
Lebanon -3
Manchester, Grenier AFB -3
Mount Washington -19
Portsmouth, Pease AFB 9

Be aware though that changing the OUTDR DSGN to a LOWER number will mean that at a given temperature your BOILER TARGET will be lower.

In this diagram, what you've got NOW is shown in BLACK. Let's say you are nearest to Lebanon and you plug in -3, that's shown in RED



If you follow the lines on the chart you can see that by lowering the design temp, your system will target a lower temperature for a given outdoor temperature.

Ideally, this is actually what you WANT to happen, and I don't know if there's a reason that your setting is such... maybe the home wasn't heating well at the lower temperatures and someone intentionally raised the design temp in effort to improve the comfort. Nothing wrong with that as long as it was done for a logical reason.

Moving the OUTDR START to a HIGHER number, you can see the result of that will be HIGHER boiler temperatures at higher outdoor temps. If your home seems cool-ish at the 'in between' outdoor temps, you might want to experiment in that direction.

Always keep in mind that you should NOT lower the BOIL MIN setting because if you do you will subject the boiler to the possibility of condensing the flue gases, and corrode boiler, flue pipe, and chimney from ACIDIC condensation. 140F in my opinion is even a bit on the low side for a GAS fired system... barely OK for an OIL fired system. I myself would not use less than 150F for a gas fired boiler. (I just went back to see what boiler you have and the MPO is FINE at a 140F BOIL MIN)

Being that I believe 10F is the DEFAULT for the control, perhaps it was never changed from that because the installer didn't know any better? Maybe you CAN heat your home at 10F outdoors with 165-ish F water... and save a few bucks on fuel.
 

Last edited by NJT; 12-05-14 at 07:22 AM.
  #15  
Old 12-03-14, 03:33 PM
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Is your sensor located at a location that is not influenced by the sun beating on the siding and giving an artificially warm reading?

I see some snow accumulation around it... is it subject to being covered with snow which could insulate it from the colder air, also giving artificially warm reading?

The ideal position is going to be somewhere that it is most likely to sense the actual air temperature.
 
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Old 12-03-14, 03:46 PM
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I also just read back to remind myself of the original problem and I think it's pretty certain that there is not enough baseboard in the bedrooms that are suffering from too cold.

But perhaps there was an air blockage since you say they are 'better' now.
 
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Old 12-05-14, 07:19 AM
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NJ Trooper, thank you again for the advice and opinion.

I agree that there's too little baseboard in the rooms and that's the main reason why the heat isn't as responsive. Since removing the air in the circuit, cleaning the baseboard thoroughly, and adding foam insulation to the copper pipes in the basement (still in progress), we've noticed a huge difference. It's still not the warmest area in the house, which I expect with the length of baseboard in the room, but it meets the temp we want in decent time.

I think the outdoor sensor is in a good place. It's not covered by snow and it's not in direct sunlight too often. The snow in the picture is the residue from me shoveling 16" of snow to get to the sensor.

The overview of the settings on the outdoor reset module is very helpful - thank you. I'm going to leave the settings as they are for now and monitor the situation, especially when we have a few days that dip below 10F. If it doesn't seem to be working well then, I will revisit the settings. I'm all for saving some money on oil if it works out.

Thank again for all of your help!

Dan
 
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