Boiler can't keep up

eastfork

We have a Lochinvar Knight wall hung Fire Tube boiler WHB085 running LP gas. It heats radiant floors in a concrete slab on top of floor framing over a 5 foot crawl space. The space heating is through 4 zones, 2 of them set at 70 degrees, the bedroom at 60 degrees, (total 1300 sq. ft.) and the garage set at 50 degrees, (900 sq. ft.). Winter temperatures stay below freezing, and get down to -20 to -40 degrees overnight. It is also responsible for DHW through an Alliance SL indirect water heater located in the crawl space.
The set-up works without issue until the overnight temp falls below -15°. During the evening it serves whatever calls it gets and maintains the system water close to set-point, but seems to fall asleep overnight and by 4am suddenly has all 4 zones calling, and the system inflow is 70° and the boiler can't catch up. Takes it half of the next day to reach set-point, depending on how low the overnight temperature fell.
All seasonal maintenance is performed on schedule, and the boiler gas valve was replaced this winter to address a chronic "flame fail ignition" issue which has not occurred since.
We'd love to hear any wisdom from those far better versed than ourselves.
Thank you.

Steamhead

Are you setting the thermostat back at night?

Dave Carpentier

Do you know what the set point is while its trying to catch-up ?
Is the burner showing 100% ?
Whats the outlet temp ?

EdTheHeaterMan

@eastfork said "but seems to fall asleep overnight"

Need more information on why you say this.

• Is it a fact that the burner stops for a time overnight?
  
• Is the burner operating non-stop overnight but the room temperature drops as the outside temperature drops?
  
• Is the burner cycling on high temperature and the circulator operating non-stop overnight?
  
• Are you actually unaware of what happens overnight and are just waking up to a cold home?
  

Without knowing what is actually happening with the burner then I can only speculate that the radiant floor heat is capable of a 80° temperature difference. That means when the outdoor temperature is -10° the indoor temperature can only reach as high as 70°, which is just fine if you desire 70°. the problem is when you desire 70° and the outdoor temperature is -20°. If you only have the capacity to add 70° then The highest indoor temperature will be 60°. (-20° + 80° = 60°). Simple mathematics.

Now do that with -40° outdoor temperature. (-40° + 80° = 40°). That is darn cold. No matter how much you operate the burner, if the heat emitter you are using can only give you an 80° increase in temperature, then that is all you are going to get.

Your Boiler may be large enough, You just need to add more radiator(s). That can be old cast iron, or baseboard, or panels, or even Radiant Ceiling heat.

To be sure we need more data on what is happening.

Mr. Ed

hot_rod

Do you know how to get into the control parameters? there is a night setback function in the control, possibly it has been enables.? Getting into the status menu would show that.

jumper

HHW can takes its sweet time catching up. May not be a matter of keeping up.
Floor radiant has heat inertia. Space cools off slower but then also heats up slower.

HomerJSmith

The boiler is only going to produce 85,000 Btu/h. At night the building heat loss may be greater than that. What you can do is increase the Btu production, new boiler and increase in radiation, or decrease the heat loss to the outside, insulate the house envelope, insulate the under floor below the pex. Insulation is the cheapest improvement of the comfort level.
If the programing is correct, 100% and no short cycling; you are squeezing as many Btu's as you can generate out of the boiler.
Look, flow is the conveyor belt that move heat energy from the boiler to the radiation (pex). Check the flow in your manifolds, loops and increase the flow, but if the boiler is running at 100% without cycling the flow may be ok even without a balanced sys. A balanced sys is important for maximum usage of the radiant sys.
You can increase the boiler water temperature which will increase the Btu into the pex and into the rooms and use outdoor reset to moderate the heat during the day and raise it at night.
Any anti-freeze in your sys? That would have a big impact on heat generation and flow.
A new gas valve requires a combustion analysis.

hot_rod

Does temperature in the home drop during the daytime if it gets below -15?

eastfork

Thanks to all for your input. We aren't manually changing the thermostats, they are always at the settings I described. Boiler always burns 100%, unless it is just maintaining a light demand, which it will do at 10%. But it will rise back to 100% as soon as the inlet water temp falls below he differential set point. What we haven't done is sit up at night with it. Everything we've witnessed occurs between 4am and 11pm, so yes we are simply waking up to a cold home, and can't be sure that the boiler hasn't shut off at some point. It seems as if that is what's happening. I will look at the control parameters and see whether it possibly has a setback enabled, and get back here tomorrow. Again, many thanks for your efforts.

HomerJSmith

eastfork, your boiler might operate at 100%, yet the limit can be set at 120 deg or 180 deg. Push the navigation button and look for SH1 heating for the programed limit. You can go into programing to increase that limit if it is too low which will increase the temperature of the water going to the manifold(s) which will put more Btus into the rooms.
You should probably have someone who knows Lochinvar program your boiler and do a combustion analysis.
What are your floor coverings, carpet or wood flooring or tile?

mattmia2

A phone or tablet recording the control panel over night could tell you what the boiler is doing. doing a heat loss calculation on the house is the other first step to see if the boiler is properly sized.

hot_rod

Do you have the model with the display screen, the Smart System?

Learn how to get in to the data menu, it is in STANDBY mode, it has a run time counter that you could check in the evening and the next morning. It will show SH run time (space heat), SH cycles,
ignition cycles, etc.

HomerJSmith

If you have the Service Manual, you can find the information that you need for programing.

Solid_Fuel_Man

If tye burner us operating at 100% all the time at 85,000 that is about 0.9 gallons/hr or propane. Does your usage reflect that? 

eastfork

Unfortunately, having now found this site and being beneficiary of all your generous time and thoughts, the reality is that winter is retreating and we've probably seen the end of conditions that would test some of the theories. -20° last Tuesday was probably it.
The temperature calculations from Mr. Ed and HJS are pretty damning, I've wondered all along if the boiler is simply insufficient.
The tech who installed the gas valve did a combustion analysis, made small adjustments, and pronounced it correctly tuned. The flame sensor routinely shows only 7-8 uA at 100% fire. I read that it should show 10 uA, but haven't any way to confirm, and seems a small detail. Changing the flame sensor had no effect on this.
hot rod: The parameter controls allow temperature changes for night setback on both SH and DHW, but there is no provision for setting On and Off times, I'm guessing this couldn't be enabled.
HJS: We have increased the SH set point from the default 125° to 135°, but don't have the confidence to go up from there, just simply don't know enough about what we're doing. No floor coverings, stained concrete. Don't understand Outdoor Reset, but we have the outdoor temp sensor installed and should be able to use that if it might help the problem.
hot rod: Great idea to just check the runtime evening and morning, the fact that that didn't dawn on me is testament to both my pea brain and to the value we're receiving here. Thanks again!

HomerJSmith

I would certainly want to check the under floor insulation and make sure the back loss to the 5' space under the floor is minimal. You can check that with an IR camera pointed up to the floor above. You want the heat energy in the living space not in the 5' space.
Heat energy goes in a straight line to what ever is coldest. UP, DOWN, or SIDEWAYS, doesn't matter. You want it to go up which is why you insulate to slow the emissions to an undesirable direction.

PS. Don't denigrate yourself. You were smart enough to come to a site that could address your concerns.
Use a laser thermometer and shoot the concrete floor. A temperature of 85-90 degs would indicate an adequate heated slab and raising the boiler supply water temperature could create an uncomfortable floor. You can't make any changes to pex encased in concrete and the hope is that the layout was properly done. You can also use an IR camera to shoot the top of the floor and see the layout.

If the floor is at an adequate temperature, the boiler is probably sized correctly and is producing enough heat energy. Sometimes increasing the flow will put more heat energy into the living space because as the water flows thru the loop it gets cooler and increasing the flow will keep the temperature higher thru out the whole loop. You can measure the supply and return temp at the boiler and determine the Delta T which is the temp difference and if the Delta T is wide you can increase the flow to narrow it which would bring more heat energy into the cooler part of the loop and thus into the living space.
Setback thermostats don't work well in your situation because of the lag time it take to heat the slab and to cool the slab. The slab is the heat emitter not the tubes.

Derheatmeister

Did your installer do a heatloos calculation?
Is this your first season with this boiler ?
Is the envelope thight ? Or do you have drafty windows ?
What is your altitude?
This boiler also needs to be derated for Altitude and the fact that it is LP Gas.
At high altitude you may only have between 60.000 BTU/HR and 70.000 BTU/HR Output...
Setback times are only availble Via the ConXus App.

eastfork

Sorry I've been absent here, and thanks to all respondents. Insulation is 1" spray foam against exterior walls, backed by R-19 bats. Ceilings and floors are R-30 bats, and crawl space walls have 2" rigid blue board full depth. Windows are not drafty, and we have thermal blinds that are down after dark. All new construction in 2019. I watch the Delta T it is mostly narrow, but can get wide when the boiler seems to be behind. Elevation is 7000' and the boiler is equipped with the high altitude control board.
Thanks to all advisors, your help is very appreciated!

eastfork

Nine months later, and we have discovered a water leak. Water is somehow entering the boiler combustion chamber and exiting through the condensate drain. Would never been the wiser but the condensate drain tube came fell away from the trap spilling water onto the floor. The water that arrives there is only lukewarm leading me to suspect it is leaking into the very bottom of the boiler and exiting right away. But it is a quantity too much to be normally produced condensate. This only happens when one zone is calling, and has a visible effect on the boiler function: it doesn't heat water quickly. Turn that zone off and the boiler function seems to return pretty quickly, other zones are satisfied, the setpoint is met, the boiler shuts down. Love to hear any comments, thank you!

mattmia2

If the boiler is leaking water will continue to come out of the condensate continuously when the boiler is off.

If that zone is far more mass than the boiler can heat, it will condense far more than usual because the incoming water never gets hot and the cooler you cool the products of combustion the more water condenses out of it.

HVACNUT

If there were a crack or hole in the heat exchanger and water leaking into the combustion chamber, then it would leak all the time. Not just when one zone is running. It would leak even if nothing was running. 
I didn't follow the whole thread but I think you made a wrong turn in diagnosing.
Do you have a service agreement with a heating company?

hot_rod

You can occasionally get a weld that opens as the metal warms but can close off enough to hold 10 psi when cold. Solder joints can also leak when warm but not cold. That could be the cause if an intermittent small leak.

eastfork

Thanks to all for your insights. Yes, the zone causing the large runoff out the trap is the garage, which is maintained 20° lower than the balance of the system, and therefore doesn't call near as frequently. I imagine that it provides a big mass of relatively cold water to heat when it does call. What's more, I think I've misapprehended what "nominal" amount of condensate should be produced in combustion. Apparently something measured in ounces, not milliliters. I'm thinking there really isn't a way around this problem, other than to maintain the garage at a temp more aligned with the rest of the system, which we don't want to do. Thank you all again and happy new year.......

ratio

How is this system piped? You didn't say explicitly, but it sounds like the boiler fires at 100% for heating & you open valves or start pumps to control the temperature? Or, does it fire at various rates, but basically go up when it's colder & down when it's warmer?

I think you might be better served by adding a thermostatic valve set up as boiler protection to handle the garage loop. That will keep a big slug of cold water from getting into the return, which by your description seem to be what's kicking off the problem; & even if it's a sizing issue, it should only help heat the house at the expense of the garage. Maybe think about outdoor reset too. ISTR @DanHolohan describing this very issue of overly cold return water overwhelming a boiler in one of his books. I can't recall how it worked now, but it made sense when I read it!

eastfork

Thanks ratio! When a zone calls, a pump circulates that zone. The boiler fires, then modulates its rate from 10% to 100% according (I assume) to the inflow temp.
Do I understand that a "thermostatic valve" would squeeze the return flow if it fell below a certain temp? Would it be located in the offending zone, or on the boiler inflow? As a trial perhaps I could reduce the pump speed on the garage zone? The zones are circulated with three speed pumps all of them set at the middle speed. I've attempted to understand "outdoor reset" from the operating manual, but couldn't make heads or tails out of it. Sorry for all the rookie questions, and appreciate any thoughts you might have time for.

ratio

Take a picture or so of the boiler, standing a little ways back so the piping can be seen. You can attach it using the li'l picture icon above the text window (4th from the right).

A thermostatic valve is a three-way valve that will adjust the percentage of the two inputs to make the output meet it's setpoint. It would be installed to keep the return water from the garage loop from driving the boiler return temp too low. Reducing the pump speed to the garage should help, good idea.

Outdoor reset is pretty simple in and of itself—as the outdoor temperature goes UP, the boiler temperature goes DOWN. To understand why this is useful, however, takes a little more understanding. A house cools off at a certain rate. This rate is based, among other things, by the difference between the indoor temperature and the outdoor temperature. The bigger the difference, the faster the house will cool off. What this means is that you have to add more heat to keep the same indoor temperature when it's cold out than when it's only cool out. The goal with outdoor reset is to add just the right amount of heat to keep the house at the same temperature. Since we're adding less heat, the pumps will basically run all the time & the thermostat will just turn the pump off if the zone starts to overheat due to solar gains from the sun or a wild party with lots of kids running wild through the house. Once the pumps are running (nearly) constant, the water temps will be more constant, the big dump of cold water shouldn't happen—but for a lower zone space temp, the zone supply water might need to be lower too. A mixing valve for the bedroom, controlled by the stat, and an injection pump for the garage; but I like complicated so take that with a grain of salt.

eastfork

Thanks again ratio, for your very patient and thorough explanations. I apologize that the attached picture isn't better, the boiler and appurtenant works are tucked into a very small mechanical closet, I got as far back from it as I could.
Before receiving your reply, I had gulped and gone ahead with two changes: I reduced the garage circulation pump speed in hopes of keeping that zone's inflow at a slightly higher temp. I also raised the space heating minimum set point from its default 60° to 85°, the idea being to keep the inflow temperature higher. I did catch the system in an isolated call for the garage zone, which was handled without plunging the system temp way down. Unfortunately, (or fortunately) the weather continues to be quite mild, overnight lows only dropping to a little below zero, which doesn't challenge the system much. Nevertheless, the upshot of the changes is that the boiler seems to run a bit more often. I can't knowledgably defend either of these actions, but as you pointed out, reducing garage flow speed seems intuitively correct. And yes, I know I've broken the first rule of the process by changing two variables. Guilty. I hope you'll alert me if the second change is ill-advised.
Once in possession of your reply, and perhaps a bit smarter but limited by my very slow uptake, I decided to not to change any of the outdoor reset parameters. The outdoor low temp seems that it might be a logical starting place, but it is set at its default of 25°, which we hit as quickly as the sun goes down.
I do appreciate your clear description that you "like complicated", I'm just the opposite, forever trying to advance with what I have to work with. Please understand however that I'm very grateful for your time and effort. Thank you.

EdTheHeaterMan

Interesting way to install a strainer. With the drain on the top. I thought that water drained down in the northern hemisphere and it drained up in the souther hemisphere.
Is your plumber from Australia?

Makes me wonder if your installer understands basic law of gravity?!? Hope his boss designed the overall system.

eastfork

Ha! Even funnier is how blissfully ignorant I am....... Always wondered what that device is.

GGross

"I reduced the garage circulation pump speed in hopes of keeping that zone's inflow at a slightly higher temp"

Less flow will only reduce the average water temperature, if you want to increase the average water temp in a circuit generally you want to increase the flow. If the changes you made work however I wouldn't worry about it too much