Easy fix for Mod Con upgrade to 2 zone baseboard convector heating system that's struggling?
I'm a long term lurker that is NO professional when it comes to HVAC but I know enough to be dangerous. My home is heated with a Triangle Tube Challenger combi that's still limping along 14 years later and that upgrade will be a different discussion.
A lady at church complained this morning that her heat went out and "they replaced the boiler but it's not working- it's only 68F in my house". She said they've made many visits since they first upgraded the boiler but the heat still isn't keeping up. The HVAC installers told her at the next visit they will be cleaning all of the baseboard convectors because that might be the problem.
I found what looks like a fairly-well installed Rheem Thermaforce 199KBTU Mod Con trying its best but just not keeping up. Both zones were calling for heat and the display read 136F and when I pressed the radiator symbol it showed the target temp was 185F.
Both circulators (grundfos) were set to speed III. There is a taco zone board managing the 2 zones of brand new thermostats that were installed at the time of the upgrade.
Convectors that I spot checked by hand were warm.
I told her to ask her HVAC contractors "if the boiler knows it needs to make 185F water why isn't it doing better than 136F?"
I think we all know that if the boiler was successful in making 185F water she wouldn't be complaining that it's too cold in her house.
Knowing that her old boiler worked fine to heat her poorly insulated house with dusty convection radiators before its death at 35 years old - is it crazy to think the HVAC installers missed something simple in the setup of the boiler? Or did they just plain pick the incorrect boiler for the application?
2 story house from 1910, less than 2000 sq ft, natural gas. Outdoor temp today is in the high teens/low 20s and this has been a rough week of 0F at night.
Thanks for any advice!
-Dylan
Comments
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Probably should have taken more photos.. but here are the 2 I have.
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68F at 136F is pretty great.
Im pretty sure the boiler needs some setting arranged.
They will need to go into the menu and up a couple values.
I have a similar boiler in my home.
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If its set to 185 and not able to get there, being that it is 199, my money is on a flow issue. are you sure the call for heat never goes away? the boiler just keeps puttering along, never reaches setpoint or fixed high limit? I'm assuming it will not go to high fire, or at least for very long. 199,000 btu/hr is a lot, much more than that house needs.
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Either the boiler is not hitting high fire, or it's simply undersized. VERY hard to believe that a 199k couldn't heat a 2000SF home, but stranger things have happened. Do we know how many BTU the previous boiler was? I'm not familiar with that Rheem in particular but most combi units have a function where space heating firing rate can be limited, and have seen more than once that somebody accidentally changed those parameters to limit the rate.
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Thanks Kcopp, GGross and GroundUp-
I agree with your input, it's hard to believe that this is the wrong boiler, it's more likely the setup is wrong.
I don't know what boiler was removed.
If there is a flow issue, the only plumbing changes from what I see are near-boiler piping.
I'm 99% certain that the tstat is always calling for heat because she had it set to 78F in an innocent attempt to warm the house. I left it alone. The weather hasn't changed much, it's still below freezing.
I'll check in with her and see if there's any news. Appreciate your input!
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Can you find this value? what does it tell you? that should show what your current setpoint temperature is
(edit ignore this first bit I re-read your original and see you pressed the radiator icon to see 185, leaving it for reference)
If the boiler is not using outdoor reset you can adjust the setpoint like this. I haven't found the instructions in the book to adjust the outdoor reset curve(edit found it). If there is an outdoor sensor installed and a curve is used you would need to adjust that value if the setpoint is too low. There is a note that if an outdoor sensor is used to "See separate controller manual for parameter information" There is a separate manual for the controller, its rather in depth hopefully you have that on site. I will link the manuals I was looking through below. If you look through the installer parameters, and advanced parameters it goes over minimum supply temps, outdoor curve, and the advanced has limiter options for the max output for space heating. that should be all the relevant parameters!
install manual
Controller menu (has outdoor reset control parameters and how to change)
I think we should confirm first without a doubt what temp the boiler is trying to make
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Thanks! I can drop by again and confirm the boiler setpoint, but it was pretty obvious to me that it was firing and the setpoint was 185F but only making 136F.
I was tempted to change the circulator speed settings but managed to keep my hands to myself. They were set to the highest speed and I'm the sort that would try the lowest speed and just see what happens after 24 hours but it's not my house or my install so I left them in high speed.
When I called to check in on her the heat in the house wasn't much different and it's still very cold out BUT she knew well enough that with electric space heaters going in most rooms that wasn't a surprise. The installer still hadn't returned to "clean the dust off".
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You should be able to get into those installer parameters without too much trouble to confirm firing rate is allowed to go to 100% that would be the next easiest thing to check. Beyond that I if the system can fire at 100%, is it actually firing at 100%? Does the burner cycle while not being able to maintain heat? If the burner does cycle we need to figure out what it is cycling due to, is a thermostat call intermittently cutting out? is a safety shutting down the burner? If the burner runs at 100% constantly and never raises the temp then the unit is too small-* This seems to be very highly unlikely* I am thinking the burner is somehow locked to a lower firing rate, either due to flow, or a programming lockout.
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@GGross thanks again for your assistance. I spoke with the homeowner yesterday and she reported that on Friday a tech visited and disconnected the outdoor reset temperature sensor and "everything worked for one day"
Saturday was viciously cold with a nasty wind chill so I'm not surprised the heat didn't keep up- 64 but set to 68.
She did report that the radiators are now HOT & that's an improvement.
I'll consider this somewhat solved for the time being. thanks again for your input!
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I might still encourage taking a closer look at some settings, the boiler itself should have enough energy to heat the building well above 64, it's possible there were existing distribution or emitter inadequacies. I know I wouldn't be fully satisfied with my own at 64… My house probably has a bit more insulation its a 70's build, probably close to the same sqft but with a full finished basement. I am using an 85k boiler main floor Central stat at 73, keeps perimeter bedrooms around 68. We regularly get sustained periods below zero, just went through about a month of it lol. Woke up to 12 degrees today and thought spring had sprung!
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so the reset curve is very wrong. it also may be going off on high limit after a short time because it is firing at a much higher rate than the radiation can absorb then staying off on an anti short cycle timer so it is off on that timer a large portion of the time. yo should measure the radiation and set the max firing rate to something close to what the output of the radiation is.
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A couple other things to remember. That is the same boiler as the IBC SFC199. The 199,000 is only for domestic water heating. The space heating side is only 125,000 btu input and at a supply temp of 185 degrees you are probably only 100,000-110,000 output. Also this is going to be at the boiler supply sensor in the boiler. If your system pump is running too fast or too slow you may not be picking up enough btus from the boiler. It would be great to know what the return pipe temperature before the closely spaced tees and how many feet of baseboard are in the system. This could give us some idea of how many btus are actually being delivered.
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Thanks guys for all the great input. I'm traveling for a while but will check in again when I am able. I know she had another call into the installer, I'll ask her if there was any new info. Great point about the DWH vs Space heating BTUs, thanks. Also good points about a possible high limit / short cycling problem.
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the heating input of 125,000 btu/ hr at 82%
should still give you around 100,000 btu/hrWhich should be plenty for a 2000 sq ft home
As @GGross mentioned, go to the control to “n” setting to see if it is at 180 for space heat mode
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
It's not the boiler size. With the BTU the boiler is capable of it should run away with that house even if the windows are open.
Some parameter isn't set right.
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