New Boiler Now Doesn't Heat well

Users who are viewing this thread

Tim Fastle

Member
Messages
45
Reaction score
0
Points
6
Location
New Mexico
I had a leak in the heat exchanger in my old boiler (38 yo Burnham 165,000 BTU gas) and decided to have it replaced. I had an HVAC contractor do it and it was replaced with a 166,00 BTU Weil McClain boiler. A pretty similar boiler with some upgrades - ignitor, digital gauge and slightly smaller footprint. Based on information here I did run through the sizing calculations using my gas bills from the past and therms used in the coldest months and it sized out to be correct (1.4x).

SHORT VERSION
It now does not heat all the zones (8 zones, 4200 sf home) very well. The closer zones seem to work pretty well, the further zones much less so. He did not purge the system after the install and said that the air valve would take care of what little air may have gotten into it during the boiler exchange. Really, nothing else is really different, just a different boiler. I wonder if there might be air in the system and that is causing the circ pump to work inefficiently and not pump well. Short of just purging it, is there indicators or a way to tell if there is air in the system? I do not hear any heavy gurgling or anything abnormal. Before the exchange I did have some gurgling and none at all now. Clearly water is circulating because some areas heat decent but none as well as before. Or is there something else I should be considering. It goes through it's cycles just fine, up to 160 off, runs for a while, down to 140, back on. Below I will post more details in a long version but I suspect this will suffice in getting my point across. Thanks.

LONG VERSION
So it went in well, runs well, nice blue flame and seems to work fine. The only problem is that when a lot of zones (4200 sq. ft house, 8 zones total, 2 banks of 4 zones, one bank in the boiler room another in a closet in part of a 6 year old addition) call for heat it doesn't seem to be able to heat all of them. For instance, I am now in my office and the base board radiator unit isn't warm at all yet the furnace is heating, the circulation pump is running and the zone valve to my office (along with 5 others) is open. I am a little bamboozled. The HVAC guy seemed to know what he was doing and did a very clean installation. Since the layout of the new boiler was very similar to the old one it didn't require a great deal of new plumbing, really just a slight reroute of the pipes that connect the water to the distribution system. It seemed to work pretty well but it didn't seem like the baseboard units got quite as warm as before and some of the further out ones, in particular, the ones in the addition don't seem to work very well at all, especially when a lot of zones are calling. Before the exchange I never had this issue at all. They all heated up quickly and there was never a problem even if all zones were calling. The recirc pump is the same size (1/25 HP) and basically the same as the old one.

The only thing I can think of is that maybe there is air in the system and this is not allowing the pump to circulate the hot water effectively. I am fairly certain he did not purge the system at all after the install. He told me before hand he would not need to since our plumbing allowed him to isolate the boiler and there would be very little water loss. I don't hear a lot of gurgling (actually did have some of that before) or any indication of air in the system but I really don't know what those indications would be. Is this possibly my problem and how might I best figure it out?

Any input would be appreciated.

Thanks!
 

JohnCT

Still learning..slowly
Messages
342
Reaction score
77
Points
28
Location
Northeast
If the boiler is cycling then it's big enough - you're just not getting the hot water converted to warm air.

Air in they system can cause uneven and weak heating, particularly on the higher floors. When I replaced my boiler, I could not get heat on the second floor until I bled the coil in the air handler.

Also, the high limit of 160 sounds low to me. I'd set it for 190F.

John
 

jadnashua

Retired Defense Industry Engineer xxx
Messages
32,731
Reaction score
1,161
Points
113
Location
New England
What's important is what is the return water temperature. Unless the boiler is designed for condensing, the return water must be high enough to prevent that, or you'll rust out the system fairly fast.

Do you know what temperature the old system ran on?

What kind of heat delivery devices do you have? Do they have air purge valves on them?

You won't get good, or possibly any, flow to branches if there's air trapped, especially higher ones which will accumulate the most air as it will rise. The air purge valves only really work if there's some microbubbles in the stream as it passes by. It cannot deal with air when it's not being moved around.

What pressure are you running the system at? What is the height from the boiler to the highest point (that can be important for the required pressure)?

To need that large of a boiler, you either have a very large home, or little insulation or lots of drafts.
 

Fitter30

Well-Known Member
Messages
2,701
Reaction score
421
Points
83
Location
Peace valley missouri
Just because a pump is the same hp doesn't mean it pumps the same gpm and head. Do have the old pump numbers and the new one. Boiler model number, tridicator gauge on boiler whats the pressure and is the.house 1 or 2 stories?
 

Tim Fastle

Member
Messages
45
Reaction score
0
Points
6
Location
New Mexico
Thanks for the replies and input.

The house is about 4250 square feet, about 35 years old, about 1/3 of it adobe. Has good wood windows but is not an overly tight house Average I would say. I tried to figure out what is the correct number to use for boiler size. What I gave was the input. The DOE is what I used for the calculations I did using the therms used, degree days and so on. I chose the DOE sizes because the service room is indoors in an insulated room. I them applied an oversize factor of 1.4. I think the original boiler was too large but I added about 1300 sf heated space and used the same boiler. I heated very nicely, cozy warm everywhere on the coldest days. Based on that I thought roughly the same size would be good but took the time to get the data on my Therm usage over the last 3 years and did the calculations using Dec, Jan and Feb in each of those years. So I had a pretty good data set and the sizing calculations at 1.4 times worked out to be about 161,000 BTU so I think I am sized reasonably well.

It is a single level home with very little elevation change. It has what I think are called Hydronic baseboard heaters (thin aluminum plates) throughout. The lines to the "Hydronic heaters" are all in the floor and on the same level except one room that goes down 1 step. The hot water out goes up about 5 feet and into the wall, I guess back down to the slab and off to the zones. The returns all come back much in the same fashion and back through the wall at about 4' where 4 zone valves are and into the inlet of the heat exchanger in the boiler. There are also 4 zone valves in a closet in the addition and they are only about 2' off the ground. Not a lot of wild elevation changes. It is a large house with some long runs but they always worked well. The pressure is 15lbs, same as the prior unit. The prior one ran shut off at 180 (it's as low as I could get it to shut off - another reason I thought it might be time for a new one), this one I have set at 160. In my reading on the subject for in floor radiant 180 is good, or baseboard 160, hence why I am at 160.

What should the return temp be? It seems cooler now than with the old one which is also why I think I have a circulation issue. It has one Air Purge valve at the highest point in the system just above the expansion tank.

I think that somehow a good amount of air was introduced into the system and it's not allowing the pump to circulate well. I agree with you JohnCT, there's heat it's just not getting out of the water I think that's because the water isn't going through the heating units at full volume and barely going through the further out ones. I recall when we did the addition, purging the long more distant runs took a little time and effort. Maybe a combination of turns or ups and downs that sort didn't just push the air out right away. It's cold but I think I am going to shut it down and try purging the zones and see what I get.

You folks see anything I may be missing?

Thanks for the input!
 

Fitter30

Well-Known Member
Messages
2,701
Reaction score
421
Points
83
Location
Peace valley missouri
Most designs for loops are 20* max would be 30* temp difference. There normally have two temperature controls a high limit set at 190*-200* then a operating control that has a off temperature and a differential for on.
Take a few pics of the boiler , piping and name tag.
 

Tim Fastle

Member
Messages
45
Reaction score
0
Points
6
Location
New Mexico
Just prior to shut off the temp differential seems to be between between 17 and 24 degrees using my infrared thermometer. This one has two knobs for adjustment, one for the "Boiler temp" and it's a digital read out which is nice. A few seconds after you set it then switches to the unit temp and it's suppose to be very accurate. The other know is called "Efficiency Adjustment" and, I gather "min" mean least efficiency and "Max" most efficiency. Originally it was in the middle but had set it to Min to see if that might help the heat. It didn't. In reading about what it does it sounded like it made the temp change more or fewer degrees. But, when I changed it the kick on was still right at 20 degrees below the shut off and seemed to be that at all settings. I can't imagine what else it could control but I doubt it does a lot one way or the other. The previous boiler had a not so precise dial in the Aquastat that you turned for a range from something like 150 - 190 and was automatically set to kick on at 20 degrees below the selected cut off temp, which it did pretty well. From what I have discussed with HVAC guys, for residential around here that is pretty standard - no adjustment for the differential in temp and it's set at 20 degrees.

I went ahead and purged all of the zones and it appeared there was a fair amount of air in 3 or 4 of them. I ran it into a bucket rather than down the drain so I could see if bubbles came up but even then it's difficult to tell for sure. I fired it back up and it seems to be working better at all zones so I suspect that helped or is the problem. Other than the circulation pump or zones clogged (which I flushed and they don't seem to be) I can't imagine what else it could be. For now I have it at 160 still but am going to try going up in 10 degree increments to see how that effects performance.

Here are the pictures you requested. The last two pictures are one of the gas connections he made. I had not looked at it before since it's in the back. It looks to be some sort of PVC pipe and it's a bit tweaked in my opinion. Could being strained like that cause a leak over time? Is PVC pipe (it almost looks like hot water PVC) approved for natural gas? Also, the transition from gas to PVC looks like a press on fitting. Is that ok? I don't want to make a stink if it's fine but if it's dangerous at all over time I certainly don't want it.

Again, any thoughts are appreciated.
 

Attachments

  • IMG_0419.jpeg
    IMG_0419.jpeg
    81.8 KB · Views: 105
  • IMG_0415.jpeg
    IMG_0415.jpeg
    72.6 KB · Views: 104
  • IMG_0426.jpeg
    IMG_0426.jpeg
    71 KB · Views: 96
  • IMG_0420.jpeg
    IMG_0420.jpeg
    89.6 KB · Views: 95
  • IMG_0421.jpeg
    IMG_0421.jpeg
    74.5 KB · Views: 104
  • IMG_0417.jpeg
    IMG_0417.jpeg
    60.8 KB · Views: 102
  • IMG_0418.jpeg
    IMG_0418.jpeg
    43.1 KB · Views: 104

Tim Fastle

Member
Messages
45
Reaction score
0
Points
6
Location
New Mexico
CORRECTION: In my above post I mentioned and attached pictures about there being PVC as part of the gas line plumbing into the unit. That was wrong and I should have looked closer at the time. That is the line to the pressure relief valve so I am cool with the hot water PVC and the slight tweak. I was surprised when I thought it was gas because the rest of the stuff the guy did was very clean. Thought I should mention it.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks