CH rads wont heat up

Discussion in 'Plumbers' Talk' started by unphased, Dec 9, 2003.

  1. unphased

    unphased Screwfix Select

    Appealing for help with CH in my house

    Some rads are heating up (upstairs and down)and others are stone cold, although feed to non-heating ones is red hot, just not going any further. Any suggestions please?

    Fernox MB-1 in system, has been flushed out, pump works fine, boiler is in the kitchen washing up...er...works fine

    RSS
     
  2. Abe

    Abe New Member

    Seems too obvious, but have you bled the air from the cold radiators? Try again even if you thought you had done it before.

    Could be stuck thermostatic valves.
     
  3. unphased

    unphased Screwfix Select

    thanks Abe..have all ready checked for air and the valves arent stuck either...anything else please my house needs warming up!!

    Cheers
     
  4. mall.

    mall. New Member

    try closing all hot rads...so pump pumps directly to cold rads,if no improvement, close remaining rads except one,basically bleed one rad at a time moving air along/out of system
     
  5. Handyman

    Handyman New Member

    I have just fixed a similar problem.....
    The system had been botched and added to then left empty for 9 months
    The boiler was an old Baxi Solo with a combination cylinder........pump was overheating, rads were up and down in temp......had bled and opened and even removed some..no joy.
    Solution......rip out the old boiler stick in a new cheap combi.....result...? Heat and hot water throughout with happy tenants......amd didn't cost the earth.
    (plus there is an extra storage space where the cylinder used to live)
     
  6. Pugley

    Pugley Member

    You don't say if this problem started when you flushed the system out?

    I have this problem each year when I service my own open vented pumped system. Because there is not a great deal of head pressure in the expansion tank air collects in the flat pipe runs and will not shift without help of the trusty hose pipe.

    Get an observer and try the following:-

    1. Connect a garden hose to your external drain cock, open it and turn the hose on until water can just be heard hissing in.

    2.Get you helper to watch the expansion tank and check that it does not over fill and flood the house.

    3.Open any motor valves in the system using their manual lever if fitted. Run the heating pump if you are happy that there is water in the boiler.

    4.Now that you have some pressure in the system open the bleed valves in those cold rads until clear water can be seen. Ensure that flow and return valves are fully open (sorry bit too obvious!)

    This method seems to work with trapped air in open vent systems but make sure you don't leave the hose on for too long and over pressurise the system.
     
  7. Pugley

    Pugley Member

    Whoops forgot the moderator for the ** symbol please read the word K o c k.
     
  8. GJC

    GJC New Member

    1. Never use the pump unless your sure the system is working, you can break them in seconds!

    2. Empty the whole system again. Close all the valves. Attempt to find out which order they fill in. Listen to them emptying.

    3. Close all the valves.

    4. Refill the system, opening the valves and bleeding as you go.

    5. Let it settle for an hourish. Bleed the system again.

    6. Run it hot.

    7. Redo the above if its working.

    8. Balance the system.

    If its not playing again........after 6, Repost.

    GJ

    Would have been easier to have it powerflushed!!!!
     
  9. unphased

    unphased Screwfix Select

    Many thanks for all your posts guys...will try it all out and let you know how I get on.
     
  10. Pugley

    Pugley Member

    1. Never use the pump unless your sure the system is
    working, you can break them in seconds!

    GJC Could you please explain what you mean in your above statement. Perhaps I have misunderstood the context in which you make this claim?

    Domestic central heating circulation pumps must be just about the most durable pumps in existence.

    - They are designed cope with being seized by debris without burning out.
    - Run for years with zero maintenance.
    - Draw only a few hundred milliamps without producing much heat.
    - Have bearings that are stainless/ceramic/bronze that are lubricated by the fluid in them and will spin for many hours after draining before binding. (the pump in question will have been in very recent use so there will be fluid in the bearings)
    - Have rotors that make no physical contact with the housing
    - Can cope with positive and negative pressures to +/- 5 bar.
    - Can cope with temps from 0 to 120C
    - Can operate in caustic or acidic environments (descalers/inhibitors).

    I have pensioned a second hand system pump off to my garden pond where it has been for the last 5 years. It occasionally cavitates and runs dry for days before I clear the air lock.

    I honestly don't see them as fragile.

    I await enlightenment
     
  11. golp01

    golp01 New Member

    A little stunt I have used to great effect in the past in this situation, is to switch on the heating. Typically it will run sucessfully for a couple of minutes and then all shut down with the boiler red hot. At this point, go to the rad furthest away from the boiler bringing your trusty 22 and 23mm spanners and a shifting spanner as well, just in case, plus two buckets.

    at the top of the rad you will see two plugged holes, open up one of them and remove the plug completely. The water will flow out of course, but after a few seconds or so, so will a mass of trapped air. Once this has gone, replace the plug. Your system should now be working properly again.

    When i do this, I use a male Iron connection with a hose attached leading out of the nearest window, plus a wet and dry vac for that belt and braces feeling.

    Please let me know how you get on.

    good luck

    pete
     
  12. GJC

    GJC New Member

    Pug,

    I know, I know. But the one thing that will ruin it is air in the system.

    These aren't 'pumps', they actually distribute the water by use of an impeller, and do not pump it. Therefore, if the impeller has no resistance, it will burn out the motor!

    Hence why the most important thing to bleed in the system is the pump, which in the main, the unsuspectings who play around with their systems, hardly actually do!!

    There again, its a quick profit when they mess it up:)

    GJ
     
  13. Dr Who

    Dr Who New Member

    Hi GLC,

    When you say that the motor burns out (para.), is this the failure of the bearings in the motor? Do they burn out because they no longer have their supply of water to lubricate them and provide a thermal exit. Therefore, causing build-up of heat in the bearings due to increased friction, which is then exacerbated by the armature spinning at a higher speed?

    thanks,

    Dr Who
     
  14. DaveM

    DaveM New Member

    Hi,

    I have a similar problem, but I don't think it is to do with air in the system.

    I had a new radiator installed under my window in the living room and had an old one removed from an adjacent wall. The feed to the new radiator runs from and existing radiator in the living room. However, either one or the other is constantly cold. All the other radiators in the house are hot as they should be, but one or the other in the living room remain cold. The distance between the feed/old radiator and the new radiator is about 10ft, and the pipe size is 8mm. My understanding is that the plumber put two t-links in the existing pipe feeding the existing radiator, which now also feeds the new radiator.

    We have tried:
    1. Adjusting all the radiators in the house to try and get more juice into the living room radiators - result was that all radiators went colder
    2. Turned the pump up to number 3 - result is that one radiator is still cold and the other is hot.

    This is winding me up. Is it a problem, or bad installation?

    Any advice would be much appreciated.

    Dave
     
  15. unphased

    unphased Screwfix Select

    Hi again!!

    I am still having no joy with my CH system. The latest was I had to replace the pump yesterday and I noticed that the pipes feeding the pump were almost completely blocked by the "black stuff". I Dismantled the pipes and cleaned them out including the Honeywell "Y" valve but my rads are still not heating up. Does anyone use the Fernox SC cleaner and neutraliser or similar and does it work?

    Cheers

    RSS
     
  16. Tangoman

    Tangoman Well-Known Member

    Hi Dave,

    my parents have the same problem in their bathroom. You have been cowboyed by the sounds of it. I'm not a plumber, and you haven't given enough info. Is the pipe feeding the existing rad > 8mm. If it is 15mm then the water won't be inclined to visit your new rad much unless it is completely switched off.

    Either get him back to sort it out or get somebody decent in to do the same.

    TAngo
     
  17. Wheel-nut

    Wheel-nut Member

    Dave, If all of you rads bar the new one are fed by 15mm and the new one is fed by 8mm, you will have to throttle back all of the 15mm lockshields to increase the pressure to the new rad.

    8mm pipe is only suitable for very small radiators and is usually piped from a manifold which tends to even out the flow to all of the radiators. This is a poor installation!

    Throttling all of the 15mm lockshields will invariably increase the noise from the pipework and may challenge the capability of your pump.

    Start by opening all of the TRV's or hand valves and closing all of the lockshields. Then crack each one open a quarter of a turn and switch on the boiler and pump. Now progressively adjust each lockshield until to get a 20 degree C temperature drop across the radiator.
     
  18. Mike Jackson

    Mike Jackson New Member

    unphased

    sounds like your system needs a proper flush through.

    Ideally it should be powerflushed but with the problems you're having I would put sentinel X400 in the system a couple of weeks before hand and let that run round first.


    Mike
     
  19. Tangoman

    Tangoman Well-Known Member

    Sounds like he already tried this approach Wheel-nut as have my parents, problem is if you crank all the lockshields down, then you restrict the flow through the entire system and most of the radiators then run cooler.

    Would be best if he simply replaced the 8mm by 15 n'est ce pas?

    Tango
     

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