New Laars combi not heating enough

[Bklynowner]

Hey all,

I'm new here. I had a boiler die during hurricane Ida. Had a new Laars combi 199k installed today. Installer said that my radiators, mostly 100yr cast iron beasts, are on tee fittings and need to be changed to make a loop - so I disconnected those tees and made a loop instead so each radiators feeds the next radiator instead. Many of the feeds are 1/2 copper with a few 3/4. He changed the inner ch set point from the factory 120f to 180f while installing. It has now been a few hours since and it seems not to work right... Temp being displayed on boiler is 140f. Thermostat is calling for heat. Pump and flame icons are on but it doesn't reach a higher temp. Radiators are warm but not hot. Not enough to bring the house to a temperature that will make the thermostat shut off (70f). I was reading manual and thought maybe outdoor sensor is preventing it but that seems odd that factory setting will be as such. It is 15f outside. Another idea is since I have such large radiators with 1/2 feed lines - maybe circulation pump isn't able to circulate it well enough? Any advice?

 

[John Gayewski]

The boiler wants to run as long as it can. Every time it starts your losing effeciancy. You said the radiators aren't getting hot, but you didn't say you were uncomfortable. Is it uncomfortable in the house?

 

[Sponsor]

 

[Jadnashua]

FWIW, unless you have a huge house, or it leaks like a sieve, or has almost no insulation, a 199KBTU boiler is likely way oversized. Industry suggests NGT 1.4x the maximum load for the 10% day. That means that extra will help when it is below normal. Keep in mind, say the house needs 100K to keep warm at -10F. If it gets to -11, instead of staying at 70, it might drop down to 69, but after the sun comes up and it warms a bit, it goes right back to where it was set by the thermostat. In the process, the radiators are running all of the time instead of running hot, turning off, then coming back on again later. As said, those cycles hurt not only efficiency, but comfort as well.

Lots of people look at the old boiler, see it's 199K, and assume they need one that size. That's often wrong, sometimes very wrong. Older installers often might put a boiler in that's 3-4x larger than necessary; might have been single pane windows that were upgraded, along with the insulation and the house was tightened up. What was, often isn't still the case.

Now, why you aren't getting a good result with what you have, not enough information to decide.

 

[Bklynowner]

OK great info here. Thank you.

John - Thermostat is picking up 69 but we like to keep at 70f (my wife...) and it won't reach it. Last night it dropped to 68. The thermostat is set to 72 so it is calling for heat all the time essentially. With my old boiler my radiators were boiling hot when it ran. Now they are warm.

jadnashua - I know. 199k is oversized the reason I went with that is that I have tenants as well (with their own ductless ac heat) and we all use the dhw together so I wanted to me sure it can make enough. My previous hot water was a takagi 199k which was able to supply us all with hot water and the laars 199k is the closest to it in terms of dhw supply. What other info you need from me to help me troubleshoot?

That is really interesting about the modern boiler way of just running hot all the time instead of the old one that kicks on and off.

I just wish for it to be a ted hotter. I am very happy with the boiler in terms of noise. It is so quiet (and the pump) that standing right next to it - I can't tell if it's running at all.

I know installer went into the factory settings and raised the CH set point from the default of 120f to 180f (max). But when the boiler is running the display shows 138-140. It won't go over that. I believe that is the water temp inside (makes sense since the radiators are not very hot). Why does it not go above is what I am trying to figure out.....

One thing I can think off is the factory setting from the outdoor sensor. I am not sure what it is set for but as far as I can tell from laars videos and manual - if the max hot temp is set for below 180 F no matter the temp outside it won't let boiler go above that. If that is true then seeing the laars video it is easy enough to adjust and I can't try that later today...

Another possible reason is that the supply line between radiators are 1/2 while the radiators are massive so maybe it is too long of a run for it to push through 1/2. But Again, it seems like the boiler itself should at least get to 180f which as far as I can tell... it doesn't.

Any other ideas?

 

[Jadnashua]

I'm not familiar with that boiler, or the intricacies of a combi that much.

 

[John Gayewski]

You need to call the manufacturer and ask them how to run it. It should satisfy the thermostat. Your wife should be comfortable. You should be able to manipulate it to do whatever you want it to do. Without someone going over the manual and learning the particulars on it there's no way to guess.

 

[Plumber69]

Was the outdoor sensor installed? If so the unit may have been preset with the outdoor sensor active. If so then this is your issue. Disconnecting the 2 wires might solve it or give you an error code. You may have to go to settings

 

[Fitter30]

Boiler on natural gas? Can clock the gas meter see if it's running at capacity. Take a few pics of your boiler and piping.

How to Clock a Gas Meter — HVAC Tech Hangout

hvactechhangout.com

 

[crugj1]

FWIW, unless you have a huge house, or it leaks like a sieve, or has almost no insulation, a 199KBTU boiler is likely way oversized. Industry suggests NGT 1.4x the maximum load for the 10% day. That means that extra will help when it is below normal. Keep in mind, say the house needs 100K to keep warm at -10F. If it gets to -11, instead of staying at 70, it might drop down to 69, but after the sun comes up and it warms a bit, it goes right back to where it was set by the thermostat. In the process, the radiators are running all of the time instead of running hot, turning off, then coming back on again later. As said, those cycles hurt not only efficiency, but comfort as well.

Lots of people look at the old boiler, see it's 199K, and assume they need one that size. That's often wrong, sometimes very wrong. Older installers often might put a boiler in that's 3-4x larger than necessary; might have been single pane windows that were upgraded, along with the insulation and the house was tightened up. What was, often isn't still the case.

Now, why you aren't getting a good result with what you have, not enough information to decide.

I have a Laars mini therm & my HVAC guy said that it's undersized. I have a 100 year old house & it's 1666 Sq Ft. It has 2 zones, 1 for a newer addition & 1 for the rest of the house. the installed boiler is 84K BTU, HVAC tech said it requires a 120K BTU minimum? The heater runs a lot, house leaks horribly (I'm working on it). Question 2 can I set the circulator pump to continue to run when it calls for heat without the gas flame heating water when the temperatiure of water is already 150-170 degrees? thanks!!

 

[John Gayewski]

I have a Laars mini therm & my HVAC guy said that it's undersized. I have a 100 year old house & it's 1666 Sq Ft. It has 2 zones, 1 for a newer addition & 1 for the rest of the house. the installed boiler is 84K BTU, HVAC tech said it requires a 120K BTU minimum? The heater runs a lot, house leaks horribly (I'm working on it). Question 2 can I set the circulator pump to continue to run when it calls for heat without the gas flame heating water when the temperatiure of water is already 150-170 degrees? thanks!!

Yeah just wire the circulator to run all of the time by wiring it to a switch. Constant circulation has its advantages.

 

[Fitter30]

No you can't run the pump 100% of the time. Minimum water temp is 130° page 13 of install manual. I don't run boilers under 140° just in case it would dip down with a big load. Here's the manual. Boilers that run all the time is better than short cycling their more efficient.

https://www.laars.com/document-library/file/1478

 

[John Gayewski]

No you can't run the pump 100% of the time. Minimum water temp is 130° page 13 of install manual. I don't run boilers under 140° just in case it would dip down with a big load. Here's the manual. Boilers that run all the time is better than short cycling their more efficient.

https://www.laars.com/document-library/file/1478

The pump can run independently of the boiler they do it all of the time. The circulator doesn't care what the temp is it just moves water. The boiler can be controlled to come on at whatever temp it requires or whatever temp someone wants.

 

[DanInNaperville]

Check page 59 of this manual (assuming it matches your model) https://www.laars.com/images/uploads/products/1318F-NH2.pdf You'll see that you have to set both the central heating max AND min temperatures or it will default to a lower temperature. If you have old cast iron radiators, this boiler (while a really good boiler) isn't a great fit for your house. Typically radiators are run at 180 to 200 degrees and this boiler is designed for max 180 but tries to run at less (so it will condense).
Either you misunderstood the installer or he gave you very bad advice. If you set up the radiators on a single loop with any of the pipes in that series being 1/2", you're going to limit flow to around 3.5 gpm. At a 20 degree temp drop you'll be delivering about 33k btu per hour. Even if you assume a 30 degree temperature drop, you're at about 50k btu. No point in having a bigger boiler than that since your circulation system can't transport any more heat than that.
What kind of boiler installer sells you the wrong boiler and then leaves it to you to reconfigure the emitters to try to make up for it? Was he a house painter who sells boilers on the side? Maybe a dishwasher repair man?
At this point, either get a different boiler or divide the house into 2 or 3 zones and run separate supply and return lines to each zone. You can run them off the same thermostat if you want to but you need to flow more water to those radiators. Either that or make sure all pipes are 1 inch or larger.
https://www.constructionknowledge.n...Mechanical/Partial_Mech_pdfs/Water_design.pdf

http://s3.supplyhouse.com/product_category_files/11448-Flow-Rate-Chart.pdf

Simplest thing to do at this point would be to run 3 pex supply lines and 3 pex return lines (flexible, no joints to worry about) - and be sure the minimum CH temp is set at its max (which works out to about 167 degrees when max temp is 180). That should let you deliver at least 100k btu.
Something like this will save you some time - https://www.acehardware.com/departm...rganic-shopping&utm_campaign=organic-shopping