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Back Boiler Question

  • 10-10-2006 9:32pm
    #1
    crosstownk
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭


    I live in a 40+ year old house. It has a back boiler - no pump - which heats the water in the HWC. It heats the water hotter than the central heating.

    So here I am, sitting in the room with the fire on browsing through boards.ie and I hear a bubbling noise. Just the odd single bubble noise followed by one or two more. Then all goes quiet for a while. I heard this once or twice and decided to investigate. I went up to the hot press and felt the pipes to and from the back boiler - the pipe form the boiler was roasting (as usual) and the return was cold - this is normal too unless the fire has been lit for a few hours. I waited for the bubble noise and when it happened it came fron inside the hot water cylinder. Judging by the temperature of the water I doublt it was water boiling.

    I've been told that a cylinder of that age would have a primatic cylinder. - scroll near the bottom. It also has a standard coil from the central heating.

    I've had the fire lighting for 2 hours, I pulled the damper out after half an hour and pushed it back an hour later when I heard the bubbling noise. The central heating hasn't been on in months and the water in the HWC was approx 20-25C when I lit the fire.

    Sorry for the long winded explanation, but my question is - What is likely to be causing the bubbling noise and is it of any danger given the age and limited technology of the system?
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Comments

  • #2
    cormac_byrne
    Registered Users, Registered Users 2 Posts: 487 ✭✭cormac_byrne


    I'm not an expert, but sounds to me like the water in the back boiler is boiling because for some reason it's not circulating properly.

    The boiler could burst / explode under these conditions.
    I believe some back boilers can exist without pumps and simply rely on the fact that hot water rises to cause the circulation.

    If the central heating and back boiler are on the same circuit they could share a pump. Maybe whatever DIYer that put it in assumed the heating would always be on before the fire is lit. Very Dangerous.

    Suggest you don't light the fire till you work out how the systems are interconnected. i.e. call a plumber.


  • #3
    crosstownk
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    The systems are not connected in any way. I have two coils in my HWC - one for the back boiler and one for the central heating boiler. The central heating is pumped. The back boiler circuit is not - it is what originally came with the house 40 years ago. I never run the hot water zone for the central heating when I plan to light the fire.

    Also I doubt if it was water boiling as the bubbling sound is very intermittent. I would imagine boiling water would sound a little more 'violent'.
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  • #4
    JamesM
    Registered Users, Registered Users 2 Posts: 1,775 ✭✭✭JamesM


    crosstownk wrote:
    The systems are not connected in any way. I have two coils in my HWC - one for the back boiler and one for the central heating boiler. The central heating is pumped. The back boiler circuit is not - it is what originally came with the house 40 years ago. I never run the hot water zone for the central heating when I plan to light the fire.

    Also I doubt if it was water boiling as the bubbling sound is very intermittent. I would imagine boiling water would sound a little more 'violent'.
    I know nothing about a primatic system. But if there is a seperate system for the back boiler, where does it get its water and if it is from a tank in the attic, does it have enough water ? Could the fill pipe be corroded and blocked.
    Jim.


  • #5
    Hal1
    Registered Users, Registered Users 2 Posts: 8,720 ✭✭✭Hal1


    The exact same happened in my house the other night. Dont need to worry though its the water left in the back boiler being burned off. It does sound like something is going to blowup but its just water being boiled. When we got the gas heating in a few years back the engineer told us that this could happen and its normal. You should have a plumber disconnect the old heating system as you have gch now. :o


  • #6
    JamesM
    Registered Users, Registered Users 2 Posts: 1,775 ✭✭✭JamesM


    Hal1 wrote:
    The exact same happened in my house the other night. Dont need to worry though its the water left in the back boiler being burned off. It does sound like something is going to blowup but its just water being boiled. When we got the gas heating in a few years back the engineer told us that this could happen and its normal. You should have a plumber disconnect the old heating system as you have gch now. :o
    Your back boiler has been disconnected and may be the residual water boiling off. His is still connected and working and should have plenty of water in the system.
    Jim.


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  • #7
    crosstownk
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    JamesM wrote:
    I know nothing about a primatic system. But if there is a seperate system for the back boiler, where does it get its water and if it is from a tank in the attic, does it have enough water ? Could the fill pipe be corroded and blocked.
    Jim.
    It appears (although I'm not 100% sure) that a primatic system has a set up that allows for expansion by venting water into the HWC. When the system cools it 'sucks' in water from the HWC. I got this info below at http://www.salamander-engineering.co.uk/technicalcentre/faq/faq.htm#primatic - scroll to near the bottom for a diagram.

    What is a Primatic cylinder?

    The term 'Primatic' is a registered trademark of IMI.
    Primatic cylinders perform the function of an indirect hot water cylinder with the primary services for a domestic heating system.

    Primatic cylinders only use one supply cistern but functions as an indirect, automatically performing the duties of the feed/expansion tank in the double-feed system.

    The working principle is based on the buoyancy of air; this considerable natural force is used to create the seals between the primary (boiler) and secondary (domestic hot water) systems.

    Consequently, there is risk of cross-contamination between the hot water discharge and the central heating system, thus the use of treatment chemicals is not recommended.

    If you only have one supply cistern, or your cylinder is marked Primatic, then you should not use treatment chemicals.
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  • #8
    crosstownk
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    JamesM wrote:
    Your back boiler has been disconnected and may be the residual water boiling off. His is still connected and working and should have plenty of water in the system.
    Jim.

    Yes, mine is still working, and I'd like to keep it that way. Simply because when I light the fire I get hot water - at no extra cost which is an added advantage to the warmth of an open fire. I know a bit about domestic CH but very little about this 'primitive' back boiler set up.
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  • #9
    don bre
    Registered Users Posts: 5 ✭don bre


    have pipe stat wired through normally open contact to feed pump ,yet with fire on ,get bubbling sound before rads get hot .


  • #10
    AckwelFoley
    Registered Users, Registered Users 2 Posts: 12,556 ✭✭✭✭AckwelFoley


    don bre wrote: »
    have pipe stat wired through normally open contact to feed pump ,yet with fire on ,get bubbling sound before rads get hot .

    Is the circulating pump on the flow or return to the boiler and how far from the boiler is the the stat?


  • #11
    don bre
    Registered Users Posts: 5 ✭don bre


    hi ,i dont know which pipe is the flow or return ,sorry ,but the stat is about two feet from the boiler


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  • #12
    don bre
    Registered Users Posts: 5 ✭don bre


    i dont know which pipe is correct one ,should it be top or bottom from the boiler ,the stat is about a foot from the back boiler and the pump is beside it ,


  • #13
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,840 ✭✭✭✭Dtp1979


    don bre wrote: »
    i dont know which pipe is correct one ,should it be top or bottom from the boiler ,the stat is about a foot from the back boiler and the pump is beside it ,

    The top pipe is the flow


  • #14
    don bre
    Registered Users Posts: 5 ✭don bre


    should the stat be on this pipe


  • #15
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,840 ✭✭✭✭Dtp1979


    don bre wrote: »
    should the stat be on this pipe

    Yes. The top pipe must also be constantly rising from the stove to the boiler


  • #16
    AckwelFoley
    Registered Users, Registered Users 2 Posts: 12,556 ✭✭✭✭AckwelFoley


    don bre wrote: »
    i dont know which pipe is correct one ,should it be top or bottom from the boiler ,the stat is about a foot from the back boiler and the pump is beside it ,

    The stat needs to be on the top pipe but the pump needs to be on the bottom near tje stove as possible. . Whats wrong is that circulation pumps push water they dont pull it.. the pump isnt able to clear the water out of the boiler quick eniugh and its overheating creating the gurgling noises.

    First try turning the pump frim speed 2 which I assume it is on to speed 3. If that doesn't work and I expect it not to..you need to move it to the bottom pipe.


  • #17
    don bre
    Registered Users Posts: 5 ✭don bre


    thanks for the help everyone ,let you know how it goes ,


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