gravity fed central heating

Discussion in 'Plumbers' Talk' started by trev1962, Dec 14, 2010.

  1. trev1962

    trev1962 New Member

    hi can anyone help please??? I have a problem on a gravity fed central heating system. the boiler is a glow worm space saver, the problem being no hot water. the heating seems fine, I suspect the mains feed may be blocked ? can anyone give me a quick run down on back feeding through the vent pipe. Would be gratefull for any help.
  2. howlsatthemoon

    howlsatthemoon New Member

    i rather think you had better look into the problem a bit more thoroughly and get the problem you suspect fixed before messing about backfeeding a system. in any case if your heating is working but your hot water is off, how does that indicate a blocked feed pipe?  have you got a motorised valve? is it opening on demand?
  3. trev1962

    trev1962 New Member

    hi howlsattemoon, thanks for that.....there is no diverter valves only a pump under the boiler. no bleed screws no air vents just the pipe work. it hasnt been serviced for years and thought it might be sludge on the hot water side, sorry new to me first system ive seen like this. any advice ??
  4. palavaman

    palavaman Active Member

    No hot water.  i suspect the mains feed may be blocked?    assuming your suspicion is CORRECT, have you been up in the loft to confirm there's no water in the  CWSC?

    it could well be an air lock.
  5. trev1962

    trev1962 New Member

    yep tried that, ball cock works but if you open a drain cock in the system the water level in the header does not go down ???? I
    should have said cold feed not mains feed. Apologies all round
  6. trev1962

    trev1962 New Member

    how would you remove an air lock with no bleed screws, would undo joints???
  7. palavaman

    palavaman Active Member

    open a draincock (how come admin allow you to use the rude word cock?) in the system the water level in the header does not go down????!    why open a draincock? why not just open all hot taps?  when you open any of the hot taps, does water flow (regardless of temperature)?

    how would you remove an air lock with no bleed screws, would you undo joints???    no, you would look for the HWC draincock, connect hose to it, then connect other end to outside tap or sink cold tap, then open cold tap to backfill the hot pipes, thus blowing any trapped air into CWSC.    Beware, you could flood the loft if you dont know what you're doing;)

    you could also connect hot hose of washing machine to cold  hose valve, then open valve to back out air lock.
  8. trev1962

    trev1962 New Member

    thanks for your help, I have only been doing what people have told me to cure me problem rather than see the doctor for it boom boom!! yep water does not flow but dribbles, will tryt your methoed and see what happens thank you .
  9. palavaman

    palavaman Active Member

    no boom boom trev, the whole place may go BANG.

    BTW, someone actually said thank you?   and even so, when he hasn't relieved himself of the symptons he is suffering:)    This realy is the bestest forum ever
  10. trev1962

    trev1962 New Member

    hi palavman, i have tried all the suggestions, got the boiler to fire up for hot water now but only stays on for a little bit then goes off??? do you think it could be the thermostat? but fires normally for c/h thanks for any help.....think i'll stick to flying fast jets for the raf, but would really like to fix this problem now dont like being beaten cheers
  11. tom.plum

    tom.plum Screwfix Select

    hi trev. i have a video that may help you sort this out, at least it will help you understand where the cold feed blockage occurs, admin will almost certainly remove the link, so go to youtube, search toms top tips then go to the 'how to remove an air loch part 2'
    http://www.youtube.com/watch?v=FqaomIQ4Q7o]link[/url]
  12. catchup

    catchup Member

    Classic cold feed blockage on F/E tank, hot water on that system works on pressure from tank. If this is anyway blocked,circulation on circs ceases. Heating will work because of pump circulating water.Boiler is switching off quick on hot water cos stat is reaching temp ie, no circulation 
  13. trev1962

    trev1962 New Member

    thanks tom plum and catchup, this is what i first thought the problem was thanks for that and the video tom plum will now look for the first tee let ya know how it goes thanks again
  14. trev1962

    trev1962 New Member

    Hi tom, sorry to be a pain, I was wondering if you could help? I  have a blocked cold feed as you said. The first tee in the cold feed is right at the back of the cylinder at the bottom, in you video you say that you can cut the pipe and cap it, then join the cold feed to vent pipe.If I did this would this help if the blockage is else where? as I can not get my hands round to try the magnet on it, i could send a diagram if it any help. the videos are great thanks nice to hear someone say it as it is, Trev
  15. gasguy

    gasguy Guest

    The "advice" on this thread is abysmal.TP &  Catchup were the 1st to get it righ, sort of, but CU's reasoning is a bit off. The domestic HW normally stops before the heating simply because the top of the circuit is HIGHER than the heating circuit. herefore the circuit is broken, but the heating circuit is still complete. If you're still confused, draw a schematic, and it's obvious.
  16. howlsatthemoon

    howlsatthemoon New Member

    why thank you gasguy for your help. we were all stuck. to be fair, the op was a little misleading.
  17. gasguy

    gasguy Guest

    HATM, fair enough, if a little sarcy!. Your post was right, and the inexperienced defo shouldn't be backfeeding.
  18. howlsatthemoon

    howlsatthemoon New Member

    sarky is my middle name boyo. glad you agree about the diyists and backfeeding! i saw a burst air sep on a system that had been drained by a builder who had then backfed it to refill rather than sort out the problem. caused a fair bit of damage.

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