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Cold water not hot

Steve EayrsSteve Eayrs Posts: 56Member
If this boiler is being cold fired, and you want to continue to do this, then you will have to delay the heating of dhw until the boiler is hot enough to make hot water, not rob fronm your inndirect.
You may have to replace the aquastat on the boiler, with a triple aquastat, and adjust the min. boiler temp a little higher, so the boiler can respond fast enough.

I don't believe it sounds like your boiler is designed to be a cold start boiler. Running it like this does not make it one. It has to have controls on it to make it work right.

Would advise running this boiler whatever why it was designed to run, or adding controls to make it work right.

You are saving nothing in fuel in the long run, if your boiler is scaling up and running poorly.

I only hope your heat zones are all high temp, and you are not trying to run this boiler for radiant floor heat, directly off the boiler, w/ no mixdown.

Steve

Comments

  • JohnJohn Posts: 40Member
    Cold water not hot

    Last week or so I had questions about my boiler, proper temperatures and if it was running efficient or not. You can see post here...http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=56752&mc=20

    I have a new topic that really related to the last round of questions. I have a cold start boiler with a boiler mate (all of the information on the boiler is in the last post, link above). The boilermate is an Amtrol Mod #WH412 41gal. My problem is after running the shower in the morning for about 5-10 min. the water quickly turns warm getting colder by the min. I do not understand why I have this problem and other people that have a cold start does not.

    I got some numbers for you. With the boiler not needing to run all night the boiler temp gets down to about 105 deg. On one hand this is a good thing but...lets continue. For this test I turn the tub water on and that runs for about 3 min then the boiler turns on. 5 seconds later the designated circulator for the domestic hot water turns on. This sounds like it is running correctly but here is the problem. The 105 deg water temp in the boiler is now running through the boilermate causing the boilermate water temp to now cool down since the boiler water is colder than the boilermate water. It takes 15 min. of the boiler running non stop to get the boilermate up to temp about 130 deg. Then the boiler shuts off then the circulator turns off 5 seconds after that.

    In the winter time this will not be a big deal since the boiler temp will never get to 105 deg. But in the summer time this is the problem I am going to have. Is there a controller or something that will stall the circulator some until the boiler gets to 140 deg or so to actually start too warm the water not cool it down. Or is there anything I can do to help this?

    Thank you very much for any information you may have.
  • Wayco WayneWayco Wayne Posts: 2,470Member
    Does the indirect have a dip tube?

    A few years back there was a bunch of dip tube failures. A dip tube is a tube at the cold water inlet that brings the water to the bottom of the tank so it doesnt dilute the hot water leaving the tank. These were breaking off and the cold water was turning to leave the tank instead of going to the bottom, thereby limiting the time you got hot water. If you have one of the broken ones they are easy to replace and only cost 5-10 dollars. WW

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  • JohnJohn Posts: 40Member


    This boilermate has the cold water inlet going into the bottom of the boilermate. So I do not think it would have a dip tube.

    Thanks
  • Things to consider...

    A sloppy aquastat can give you a cold shower. If the differential is set too high, or the aquastat is just plain sloppy, by the time the aquastat wakes up the boiler to do its thang, you're already running out of hot water, and the system as a whole is playing catchup.

    High mass boilers have to get THEIR mass together before they can generate heat to clean up your mass... Time lag equals running out of hot water.

    The heat exchange coil on the indirect COULD be lime scaled up, acting as an insulator, causing the boiler to struggle to get the heat transferred from the boiler water into the potable water.

    The flow rate of your shower head could also be an issue. When considering the weight of the train you are trying to get started from a dead stop, if your shower head is flowing at an excess rate, it could be exasperating the whole process.

    If it works out that the coil is not slagged, and the pump transferring water between the two is working good, and the aquastat is not sloppy, but the boiler is high mass, you could

    A. get rid of that peice of cast iron and replace it with a high efficiency (take your pick) low mass model and watch your hot water problems go away and take 30% off your fuel bill... or

    B. Put a timer in the DHW circuit to act as an anticipator to get the boilers mass up and running in advance of your imparting a load upon it, or...

    C. Turn up a heating zone 5 minutes prior to taking a shower, then turn it down right before getting into the shower.

    You can diagnose the possibility of a slagged coil by doing a constant flow test on it at a low flow rate. Flow the water at say 2 GPM, and note the temperature continuously. If it continually degrades, your coil needs delimed.

    If the coil is not limed up, then you can diagnose the circulator function with a cold tank, hot boiler test. Disconnect the tank thermostat wires. Exhaust the tank of ALL hot water. Re-connnect the thermostat wire and watch the differential between the boiler supply and return. If it is between 10 and 30 degrees F, you have good flow.

    Watch the final temperature. If it shuts off at the right point, and turns on at the right point, your aquastat is OK.

    You've got lots of homework to do....And you thought summer vacation was just beginning...

    ME

    EDIT: After heaving read your last weeks post, you have a cast iron boiler, and it is oil. Your options for a high efficiency boiler are very limited. You're already at 86%. Look to the other options I quoted, and I am certain that I missed something that others will chime in on.

    Be sure and purchase some bricks on your way out the door :-)

    ME
  • Paul FredricksPaul Fredricks Posts: 88Member


    Since the boiler fires, then the circulator kicks in 5 seconds later, it sounds like you are feeding the boilermate through a zone valve. Make sure the zone valve is designed for high flow. It should be either a high flow zone valve or a dedicated circulator.

    However, if the boiler temp isn't there that will just allow more cool water to pump through the coil until the boiler gets up to temp. I'd look at the shower head flow first, the the coil test as Mark stated.
  • JohnJohn Posts: 40Member


    Since I have a cold start boiler I do not think I have an aquastat differential issue here. Since this system is new (2 months), is it possible for it to be lime scaled up?

    I currently have very low water pressure so my flow rate is not very high. I will fill up a bucket and see what it really is just to make sure.

    I am not sure what is considered a high mass boiler but this boiler water content is 10.5 gals.

    To answer Paul’s question about if this is on a zone value the answer is not. It has its own circulator.

    Thanks for your help!
    John
  • JedJed Posts: 781Member
    10.5 gal

    10.5 gallons water content for a cold start cast iron boiler is not efficient, or true "cold start" boiler application (assuming approx. 100,000 BTU/H). Yes, you are cold starting the boiler, but it is not a "cold start" boiler ( especially if it is a pin type boiler). A cold start boiler will hold half that or less water. You're describing a classic mis-application of "cold start" boilers. Reverse transfer in your Boilermate can be the only result. Delaying the DHW circ. will correct that inefficiency, but will not correct you're overall system inefficiency for "cold start" system design.

    IMHO

    Jed
  • J.C.A.J.C.A. Posts: 2,981Member
    John,

    Question #1..How old is the Amtrol?

    Question #2.. are you on town water or a well?

    Question #3..Have you had the water tested to find whats in it?

    My experience with the Amtrol tanks...is that the tightly wound coils...along with the slightly spaced "fins" of said coil..open themselves up to what I describe as "sedimentary collection". The 1/16th of an inch ..or less....on the coil piping gets filled with whatever comes along with the incoming water.

    Let's talk physics for a bit. When that water comes in...it goes into the tank , to be heated. When it's drawn off, it leaves the tank to your favorite fixtures.

    Now think about the "in between".

    This ..bottom line... is a Thermos bottle. It's meant to hold heat, while not being used...but make it while it's in use.

    When the incoming water sits...like your soup or coffee...during the time it isn't being used, it settles.

    The "stuff" that comes in with your water, settles to the bottom of the tank..OR, wherever gravity dictates. If gravity says it falls on the fins of the coil....that's where it falls.

    Think about this....at this point, NO water is moving through the tank. All the stuff that got into it has fallen into either the bottom...to be stirred up when the "bell fitting" in the feed/bottom of the tank stirs it, or has settled into the fins of the transfer coil.

    Add heat....now those fallen incoming "stuffs" stuck in the coil, have started to make their own little universe. Pretty soon...they have filled the spaces between the fins, and have effectively turned the tightly wound (and undersized...may I add)finned coil into a pretty much "solid coil or "fin less" coil.

    See where this is going? Diminished transfer = crappy recovery. That tank...in a perfect world, would rise from incoming temp. to set temp , depending on where you are and the incoming water temp. in a "by the book"...17-22 minutes.

    I know this is long winded, but FACTS is FACTS.

    Not the best design, but fixable. It takes some time and effort...and as long as the outside of the tank is "room temperature" to the touch...I've had good success cracking the coil clean.

    If you feel the water temperature from the tank anywhere on the outside of the tank....it has failed.(WHEW)

    Oh yeah...Reverse flow/heating WILL occur when the water in the tank is warmer than the boiler water. (low mass and HIGH temp. rise rule here) Chris
  • LeoLeo Posts: 22Member
    Good Suggestions

    John,

    You have been given good suggestions. To rule out a dirty or limed coil the question is, has it ever been right? You stated the house is new. Dirty coils come with time, that is you see a decrease in hot water over time as the coil scales up. If it has never been right follow the other suggestions.

    Another thing, make sure the boiler has the right nozzle. Some guys down size it thinking they will save oil. In some cases the boiler works harder actually using more oil. This is something to have your heating guy check and at the same time the combustion efficiency can be checked. If the heating guy does not use instruments to check combustion find one that will.

    Leo
  • JohnJohn Posts: 40Member


    This is a brand new construction house so the boiler, boilermate and the well is brand new, 3 months of use max. The water temperature was not a problem when I had the boiler running for hot water baseboard heat but now that the heat is now off I am having this problem. It takes the boiler about 15 min. to satisfy the boiler mate (this is when the boiler has not run all day 105 deg or less). In the 15 min time that the boiler has been running the boiler gets to about 175 deg.

    When we moved into the house we had a lot of sediment that was coming out of our well so after dealing with the washing machine filter clogging up for about 4 weeks I added sediment filter. This filter helped a lot. I am guessing now from what you are saying, I probably have sediment on the bottom of my boilermate which is possibility causing most if not all of my problems. I never thought of that until now. Thanks for the information and I will let you know how much sediment I get out of the mate.

    Do I need a special controller to delay my circulator until the boiler gets up to temp? I think this might help a lot too.

    Thanks
  • J.C.A.J.C.A. Posts: 2,981Member
    Brother Leo brings up GREAT points!

    If the installer decided to down fire the boiler....it could effect recovery times significantly.
    As to a clogged coil...If you had to clean the washer screen 4X in the first few months of living there....chances are that the coil has some sediment built up in IT. Drawing off the bottom of the tank will show you what is sitting at the draw down valve, but doesn't come close to show what's happening in the coil.

    Coil cleaning is a whole different procedure. It takes a true pro, and some time...(I allot 2-3 hours), to get it right...along with a small investment in valves, to make it easier and quicker the next time it happens. If it happened in the first 3 months...I can assure you...it WILL happen again.
    I wish I could say what I really feel....but I don't want to make the gods unhappy. (nuff said) Chris
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