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question on a boiler and high limit

oreo123
oreo123 Member Posts: 44
A plumber friend installed a boiler and asked me to look at it with him today. He thought it was a relay issue.

Six zones. Forced hot water. Gas. Big brand name.

The problem was only one zone (#1) was not allowing the boiler to go to high limit. All other zones the boiler would cycle between 160 & 180... I saw that a new replacement pump was installed on the loop which would not allow the boiler to go to high limit. I verified on the controller that when just zone 1 was calling that t / t was closed to the boiler its not a controller issue.

Zones # 2-# 6 are all 3/4 inch with baseboards and one radiant. They work just fine, boiler cycles, and they produce the needed heat.

I closed the valve to zone 1 half way and then the boiler started cycling bet 160 & 180. Obviously a 0010 is the incorrect pump. Now the question - if a pump is pulling water too quickly out of a boiler why wouldn't it still go to high limit?

Comments

  • Ironman
    Ironman Member Posts: 6,563
    We really need more info: boiler model and size, the size of zone one's piping and emitters. Some pics or a diagram would be helpful.

    It may not be the pump at all. If the zone is pulling a large amount of btus, then it may take the boiler a considerable time to reach its limit. A radiant slab can cause a boiler to run for hours before reaching its limit. So can a system that has a lot of mass like an old gravity system. Closing the valve down is simply causing less (or no) btus to leave the boiler resulting in it reaching its limit quicker. A large fan coil could also cause the same symptoms.

    Maybe a leak on that zone?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • unclejohn
    unclejohn Member Posts: 1,749
    Is the homeowner complaining of not enough heat in that zone. If he's not complaining go home all is well.
    Ironman
  • oreo123
    oreo123 Member Posts: 44
    More...

    I did NOT do this install. I just showed up to give a second opinion.

    Its a burnham ES2 5B. It works fine for the other zones. Put another way - ALL of the other zones result in the boiler going to high limit. Zone #1 is the only one that keeps the boiler from going to hi limit.

    I see a thrush valve on it. My guess is its a flow check an ancient one.? Pix are attached.

    Pumps are on the return side :-(

    I will try to write up the plumbing diagram later on tonight. You can buckle up for that... The "bad zone #1" has 6 radiators off an 1 1/4 loop (zone 1).

    If I did this correct this is the zone #1 rads btus. I hope that I am way too high with what I got:

    height columns edr btus

    32 10 43.3 7361

    26 22 77 13090

    26 22 77 13090

    26 20 70 11900

    26 18 63 10700

    26 18 63 10700

    66841

  • unclejohn
    unclejohn Member Posts: 1,749
    I believe that boiler is rated 105K in. So I still see no problem here unless the zone doesn't heat. If it won't heat the space the issue is outside the boiler room.
  • unclejohn
    unclejohn Member Posts: 1,749
    I can't see the piping at the boiler. There is a new copper pipe going to the air separator and it looks like it is teed into the old steel pipe. Is that a primary loop? Where are the pumps.
  • oreo123
    oreo123 Member Posts: 44
    Boiler is 140 / 118 output.
    I did NOT do this job.
    Plumber slid the boiler under existing loop plumbing.
    Pumps are on return side.
    From boiler its 1 1/4 up to a T. To left is air scoop and exp tank. Then there are zones 2-6. They all work fine. Zones 2-6 all call in boiler which cycles 160-180 when called.

    And for zone 1. The issue is the boiler has t & t closed but never gets above 150 degrees. I suspect that if the rads are not drawing all of the btus from the boiler it should go to high limit. (If any other zone comes on that boiler goes to high limit and cycles correctly.)
    Zone 1 supply comes off boiler, T's to that thrush whatever. Then it supplies 2 loops in the basement. Each loop feeds 3 rads upstairs. All of the supplies to the rads are not monoflows, instead the t's drop it down a size.

    All the rads connect back to basement loops, then to 1 inch, then the circ, bleed down, and shutoff. And then to ez header.

    I closed zone 1 valve by circ to half and the boiler goes up to high limit *assuming just zone 1 is calling*.

    Closing that valve to say half: I am sure that it cuts the flow. Does that change head?

    If water goes too quickly through a boiler - doesn't the aquastat adjust accordingly for temperature? I suppose that is a question for Burnham tech support.

    Homeowner claims the rad zone (#1) worked with the old oil boiler.


    imageimage
  • FranklinD
    FranklinD Member Posts: 399
    What I see there is that the original cast iron radiator system is zone 1, and I'd bet that the other 5 zones are all 'microzones' in comparison. If zone 1 is getting to 150/130, I wouldn't worry about it...that's a LOT of iron to heat. I have an old cast iron radiator system and a burnham esc4...the system side rarely tops 120*. Ever.

    The burnham should be good down to 110* return water, according to the literature. If your temps are above that, you're good. All those radiators are dumping heat almost as fast as the boiler can make it, which happens with that much mass.

    What are the other 5 zones connected to? Individual rooms, toe kick heaters, etc?
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems
    Gordy
  • FranklinD
    FranklinD Member Posts: 399
    Edit: I see the other zones are fin tube and one radiant...but I bet they're relatively small, and have similarly low water contents, thus giving the boiler the ability to hit high limit. The cast iron system holds quite a bit more water than that. My system is a total of 431 EDR and holds 120 gallons or so...takes awhile to heat that much water.
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems
    Gordy
  • Aaron_in_Maine
    Aaron_in_Maine Member Posts: 315
    Why didn't he get rid of that thrush valve and just pipe it in like the other zones? When I do a job I only leave the pipe all the valves flow checks exp tank etc hit the scrapper. How can you warranty work when you leave a valve put in 40 years ago and not sure what it does.
    Aaron Hamilton Heating
    [email protected] yahoo.com
    (207)229-7717
  • Gordy
    Gordy Member Posts: 9,514
    One word " Mass" @FranklinD is right on.
    Ironman
  • hvacplumber7
    hvacplumber7 Member Posts: 15
    Just a stupid question. What was the size of the old boiler? If it was way oversized, that is probably the reason the old system worked just fine.
  • oreo123
    oreo123 Member Posts: 44
    I agree with the mass idea.
    I was there and watched it only get to around 135-140 with just the rad zone (#1) running. We flipped on another zone with around 20 feet of baseboard and the output temp on the boiler climbed right up to proper cycling temp. There was more output and it climbed. Next we tossed on all zones and it was cycling up to high limit.

    What if there was a small amount of air in there - how would that affect the internal high limit?

    Homeowner is saying its taking 4 hours to warm up on the rad zone. And he only sees it go to high limit it any other zone is calling.

    Other zones are: 1 radiant (kitch 20 * 25) and a bathroom; 2 zones are baseboard (did not measure them), 1 for a garage overhead heater, and another garage heater. All other zones (2-6) when running alone bring the boiler up to high limit. All other zone2 (2-6) when calling bring the boiler up to high limit. And when ALL

    Zone 1 will not allow the boiler to go to high limit. Putting other zones on and it goes to high limit. Heating the mass AND the other zones I could see it running at a lower temp but that added load makes it cycle all the way to 180

    Then while only running zone 1, when I closed the ball valve by the pump to half - it goes to high limit.
    The way its plumbed the air float is not in that loop.

    I fully agree with that poster above to rip it ALL out. And do it right the first time. Put the pumps on the supply side too. And rip out that antique flow check (and take it apart to see how its supposed to work).

    I will try to call Burnham in the morning. I want to know if flow affects high limit.

  • Steamhead
    Steamhead Member Posts: 14,840
    edited February 2016
    You have 393.3 square feet of radiation on that zone, and you're pumping it with a Taco 0010? That's a lot of circ for that amount of radiation. I bet the water is moving so fast when only that zone is on that it simply doesn't pick up a lot of heat in the boiler.

    Does the stack temp go up when only zone 1 is calling?
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,313
    edited February 2016
    I think zone 1 is fine. If I had to diagnose this I would go zone by zone and figure out the proper flow and head requirements. I'm leaning towards the other zones being over pumped, and robbing flow from zone one. If you rob flow from zone one and your other zones are over pumped, I think the btus aren't going into the zoned spaces, just circulating thru the zones and back to the boiler, raising the boilers temp to high limit-the boiler is putting more btu's in then the smaller zones can take out.
    I would also get my meter with 2 k-type clamp on's and check supply and return temps on each zone, and what happens to the SWT on zone 1 as other zones come online.
    steve
  • oreo123
    oreo123 Member Posts: 44
    when just zone 1 is running the stack temp never goes above 145. So it takes hours to heat up the mass.
    When the other zones come on the temp climbs to 180.
    When I closed the valve by half on zone 1 it ramps up to 180.
    I guess its a physics question now. If water goes through a heating device (boiler) at a high rate of speed does it absorb more or less btus?
    I just texted the plumber for the old boiler name and size.

  • oreo123
    oreo123 Member Posts: 44
    I will try to figure out the head for the pipes and fittings. Does anyone know how to figure head on rads?
    I think that the answer will be a taco 008. It has higher head and lower gpm. The orig set up had that 0010 pump in this loop.
    Plumber is asleep and will not get back to me tonight.
    More on this as he / we dig deeper into this.
    Thanks all!
  • Ironman
    Ironman Member Posts: 6,563
    What's the delta T on zone 1? Have you tried slowing the pump to speed 1?

    The boiler has two totally different types of heating systems married to it, but apparently lacks the expertise needed to make them work in harmony.

    Steamhead's right: that's too much circ for that zone because there's very little head due to its large pipes. Look at the pump curve for the 0010. You're probably pushing over 25 gpm through that loop if the circ's on high speed.

    Cast iron rads = almost 0 head; large pipes = very little head; cast iron boiler = almost 0 head.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • oreo123
    oreo123 Member Posts: 44
    pump is one speed :-(
    I closed valve half way and right away the temp jumped up 10 degrees (within 10 seconds) and climbed to high limit (in a couple of minutes). It has to be too much water flow, too fast through the boiler. Guess I forgot that stuff from physics many moons ago.?
    I need better pipe lengths & fitting sizes to figure the head.
    In the past couple of hours I have been reading about head formulas.
    I hope that we don't cook the 010 pump being that its half closed.

  • Gordy
    Gordy Member Posts: 9,514
    You diagnosed, and answered your own question in your original post.
    When you throttled the flow the boiler hit high limit. That tells you the flow is to great.

    If you pass your hand over a flame quickly you won't get burned. If you pass your hand over the same flame slowly guess what.

    The water is making 1000 laps to get heated verses 50 at slower flow rate.

    Now you have to size a circulator that will give the proper flow. Preferably not so slow the boiler bounces off high limit cycling to death before zone is satisfied.
  • Steamhead
    Steamhead Member Posts: 14,840
    edited February 2016
    oreo123 said:

    when just zone 1 is running the stack temp never goes above 145. So it takes hours to heat up the mass.
    When the other zones come on the temp climbs to 180.
    When I closed the valve by half on zone 1 it ramps up to 180.
    I guess its a physics question now. If water goes through a heating device (boiler) at a high rate of speed does it absorb more or less btus?
    I just texted the plumber for the old boiler name and size.

    Way too much flow and you just proved it. That low stack temp is causing some major condensation in the flue- not good for the boiler or chimney. When the other zones call it reduces the flow through zone 1 which corrects the situation.

    Try a Grundfos UP-15-42F on that zone. I bet it heats faster and the boiler starts behaving normally. If you can't find that Grundfos a UP-15-58F or Taco 005 would be my next choice.

    And just to be on the safe side, make sure the boiler's gas input is right.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    SWEI
  • hot_rod
    hot_rod Member Posts: 15,033

    Those that have concluded the flow rate is too fast and the fluid is therefore unable to pickup the BTU's from the boiler are making a grave error.

    If the fluid is not accepting the BTU's from the boiler, the result is that HL will be reached faster. The boiler will not be in a situation where HL cannot be achieved.

    By throttling the flow, the OP reduced BTU's to the zone, and the boiler responded by climbing to HL.

    Should the OP install a smaller pump, the boiler will probably achieve HL, however the zone will take longer to satisfy as fewer BTU's are being delivered due to the lower flow rate.

    The OP's current situation where the boiler runs continuously while the call is present is desirable and should be maintained.

    If you need further confirmation of the above, check out your flow rates and DT's on the primary loop of your mod-cons. They're flowing at a ridiculously high rate and the fluid has no problem picking up the BTU's despite DT's that are down in the weeds.

    Exactly, BTUs and fast moving trains.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    Pumping in perspective:

    The ES25 has a DOE output of 119k.

    We installed a mod/con with a DOE output of 154k on a recent gravity conversion. System is direct-pumped by a Taco VR1816F running at the lowest (~5 feet of head) constant pressure setting. The system works fabulously.

    Once you remove the variable flow rates that gravity circulation provided, you really need to manage the water temp. IME, full ODR (down to 88 - 90°F) is pretty much mandatory to make high mass systems behave well. You may want to think about some kind of mixing strategy.
  • oreo123
    oreo123 Member Posts: 44
    Update all:

    Temperature was read from temp/ pressure gauge right on boiler supply. I verified it being correct with a handheld meter / thermocouple.

    I called boiler manufacturer and was told the following:
    boiler needs minimum temp of at least 140 on return side. This was my biggest concern when I saw this yesterday.

    He also agreed with the posters above that the mass of the large pipes that is the big load.
    He suggested a variable pump on zone #1 with an internal delta.
    He told me who makes them. I read that they can work on the return side.

    I passed the info along to the plumber who did the install. I still do not have an accurate blueprint of the plumbing in the cellar ceiling to do the head. I do remember there was quite a bit of 1 1/4. 1 pipes. Today I found out that each of the 6 rad risers to first and second floor are 3/4 and not half inch. His next visit there he will get me all of the pipe lengths and diameter.