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No domestic hot water from oil fired on demand boiler

We just bout a house and the very first night there we have no hot water. It is a Neil McLain boiler that is most likely closer to 20 years old. It heats the house great but domestic hot water is only hot for about a minute then it goes cold. I felt the hot water supply pipe coming coming out of the boiler and it is cold. Not as cold as the cold water going in but by no means hot or even warm for that matter. This morning we turned up the heat in the house and used the sinks about 20 minutes later as we had plenty of hot water. Ow this afternoon we are back to no hot water again. What could cause this?


  • JStarJStar Member Posts: 2,668

    The coil that makes the hot water could be dirty. These tankless coils are notorious for lacking any kind of satisfying hot water production.

    The grey control box on the front of the boiler has a dial inside that sets the low limit temperature. Have you looked inside of that control?
    - Joe Starosielec
  • JhoffmanJhoffman Member Posts: 5
    edited February 2013
    No domestic hot water from oil fired on demand boiler

    I just went down and took the cover off. I don't see a dial but it has a digital display that is flashing three different things but I think there may be some segments burned out on the display because one of them doesn't make sense. They are: 6?, 184, and *F. I can add pics of the display when ever my photo stream decides to update to my pad. Can't tell how to adjust anything.
  • icesailoricesailor Member Posts: 7,265

    I just wrote a long answer to this but it didn't post.

    Your problem is more likely that the boiler controls are wired wrong. You have two circulator zones. One controls the grey box in the front. The other is controlling the one on the side. The one on the side doesn't communicate with the one on the front. If one thermostat starts the burner and the other does not, it is wired wrong. Look inside the grey box in front. There will be two thermostats to set. Set the "Hi" or "High" to 200. Set the "Lo" or "Low Limit" to 180 degrees. If the circulator that is being run by the grey box on the side is calling for heat and the front one isn't, you won't get hot water.

    There is also a valve on the side down close to the floor with three pipes going into it. Some of us always install a valve there. You don't have one. The valve is piped properly but may not be working.

    More likely, it is an electrical mis-wiring problem.

    Hopefully, this will post.
  • icesailoricesailor Member Posts: 7,265
    That's different:

    That's different. I can't tell you off the top of my head how to set that control. You need to find the instructions for it. It is actually easy.

    The three white buttons are what you need to push. I think that two make it go up and down, the other one changes what you are trying to change.

    It looks like it is set to 184 degrees, high limit. The other range that is shown might mean that it is set as a "Cold Start" and only comes on when the boiler water is 0F degrees but you need the instructions. Its actually easy to change. It is possible that when that control was installed, it was never adjusted properly from a lack of understanding. It is not the original control judging from the age of the box on the side and the age of the boiler.
  • JhoffmanJhoffman Member Posts: 5

    The previous home owners just had over $600 worth of work done to it at me request due to some leaks the home inspector found. I'll see if this controller was messed with.
  • icesailoricesailor Member Posts: 7,265

    You won't know. It could have been messed up for years in my experience.

    You need to find the installation and operating sheet for that control.

    Look inside the front box. You will see two terminals that are marked "ZC" and "ZR". If both terminals don't have wires on them, the controls are wired wrong.
  • JhoffmanJhoffman Member Posts: 5
    Checked limits

    I just went done and went through the service records, the controller was replaced in 2011. Nothing has been done to the controller since then. It seems like the domestic hot water problem is tied to the second floor heat because the first floor is calling for heat and the boiler is firing and hot water at the tap only lasts about a minute and then goes cold. This morning when we had second floor heat on we seemed to have hot water at the taps. I wouldn't think it would have been miss wired for 2 years, they wouldn't have had any hot water in the summer months. I'll experiment with turning p the second floor heat again in the morning and report back tomorrow night with my findings. I was able to figure out that the high limit is set at 180 and the low limit is at 160.
  • JhoffmanJhoffman Member Posts: 5
    edited February 2013

    Every terminal block has a wire going to it. Here is another pic of the wires. I can't find any manuals, just service records.
  • STEVEusaPASTEVEusaPA Member Posts: 1,574
    edited February 2013
    here ya go

    Start out with your low limit on 160, hi on 190, diff at 10 degrees.  If this doesnt help, time to bring in a pro. Could be limed up coil or bad thermostatic mixing valve.
  • icesailoricesailor Member Posts: 7,265
    No domestic:

    Unless all that tankless heater piping is all disconnected, you DO have a working tankless.

    Unless you have a separate electric water heater, that control is what controls your hot water.

    Below is the manual for that control or one like it. It is not recommended that you futz with it. But it explains how the adjustments are made and the wiring diagrams. Its easy to get it screwed up. You need a pro. If you can find one.
  • billtwocasebilltwocase Member Posts: 2,385
    edited February 2013
    easy to find out

    by holding all 3 buttons in at once, you will be in  the "I" mode of that control. By pressing the "I" button, it will scroll thru all the settings. The other 2 buttons have arrows to make adjustments. This needs to be set closer to 170 LO, and 190 HI limit. Also, the switching relay mounted to the side is could be another problem. Pull the cover off and take a pic. I'm sure the coil is also on it's way out giving it's age. May be time to spend some money. I would hire a pro to check it out
  • Kissed2manyfrogzKissed2manyfrogz Member Posts: 1
    Same Problem- HELP

    I am having the SAME problem with my rental. The handyman has gone through the same things to try. Now I am told that the issue is that I am using a pellet stove as my main source of heat, not the boiler and that is leadig to the lack of hot water since the boiler is never kicking on. With that logic, I will never have hot water in the summer when the sun tells the boiler not to kick on and heat the house as well. HELP. I just want a hot shower...
  • icesailoricesailor Member Posts: 7,265
    Hot water:

    If the boiler is a "warm start" and maintains 160 or 170 degrees when not getting a call for heat, you should have hot water.

    Post photos of the front of the boiler. You should have hot water
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