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Vokera Compact 24 Combi - very low DHW pressure - help!!!

Discussion in 'Plumbing and Central Heating' started by jsstevenson, 6 Apr 2006.

This topic originated from the How to page called Problems associated with noises from the central heating system.

  1. jsstevenson

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    Hello...

    I have a Vokera Compact 24 Combi Boiler that I am having a couple of problems with...

    (1)Intermittent hot water then getting cold and then heating again, and so on.... - I suspect that this due to the secondary thermistor, however the real reason I write here just now is to do with my second problem...

    (2) I am experiencing very low domestic hot water from the boiler (it has never been good) - I am getting 2 litres per minute so it is barely on! I only get this much if I open the hot water tap fully - if I do not open the tap fully it trips the boiler (I believe this is called \\\'lock-out\\\') - If I adjust the dial on the control panel of the boiler for the heat of the hot water it makes no difference to the pressure, and equally if I adjust the isolating valve supplying cold water (from the rising main) to the boiler it makes absolutely no difference - i.e. opening the isolating valve fully produces the volume of hot water previously mentioned!!!

    Does anyone have any ideas how to resolve this pressure problem - I live in a tenement flat so plumbing is all on one level. The cold water rising main pressure is very good, and the DHW pressure problem applies to all hot water taps!

    Many thanks in advance for reading and commenting.

    Jamie

    p.s. I was wondering if it was potentially what the boiler manual refers to as the \\\"Water Flow Restrictor\\\" which I assume to be an insert into a 15mm pipe within the boiler that reduces the internal diameter of the pipe thus in effect reducing the water flowing into the heating chamber and therefor pressure (if this in fact does reduce pressure!!!!???) - if so, is this removable?
    Thanks
     
  2. EliteHeat

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    You almost certainly have a blocked secondary heat exchanger. Quite simple to replace.
     
  3. Gasguru

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    Eliteheat this boiler has a bi-thermal heat excahnger ie no secondary exchanger


    Check flow valve (normally square looking) on right hand side of boiler underneath is fully open

    If it is then:

    Look at right hand side of heat exchanger. The rear pipe conection will have a flow restrictor. Remove centre part and O ring - you will need a new 1/2 fibre washer.
     
  4. jsstevenson

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    Wow - incredibly fast reply - is this an expensive item?
    Thanks for your help.
     
  5. HarrogateGas

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    This boiler does not have a secondary heat exchanger. Is the isolation valve fully open under the boiler? Its got a black knob on (i think its on the left, underneath) it works like a tap, try turning fully anti clockwise.
     
  6. Gasguru

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    Washer may be free if you talk to merchant nicely, otherwise about 10p
     
  7. HarrogateGas

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    Beat me to it GasGuru!
     
  8. jsstevenson

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    Flow valve is fully open - positioned at rear on far right underneath the boiler.
    Thanks again!
     
  9. Gasguru

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    Is there a compact out there that doesn't have a blocked restrictor!
     
  10. HarrogateGas

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    yes the one i installed for my brother in March 2004!


    I must have installed hundreds of these over the years and never have had a blockage.
     
  11. jsstevenson

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    So here is what might be a very dumb question!!!!

    When I remove the flow restrictor is it sufficient to isolate the boiler cold water supply with the hot water taps open to drain the DHW pipes or do I infact need to isolate and drain the entire central heating system as well?

    Thanks!!!!!
     
  12. HarrogateGas

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    Just te coldwater and the dhw tap open.you may get a small dribble out....depends where the boiler is located
     
  13. jsstevenson

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    WOW - My DHW has been transformed!!!!! I now have hot water delivered at pressure - I thought my Combi fed shower was good before, now I'll need to install some structural steal beams to support the shower base under the pressure of the water from the shower head!!!!!

    Removing the flow restrictor even seems to have fixed my problem with the varying heat of the DHW (I hoped it would as it seemed reasonable that if there wasn't enough water going through the boiler it would cut off the burners to prevent damage).

    Thank you very much to everyone who commented - CHEERS!!!!!!!
    Jamie.
     
  14. delitubby

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    can someone explain exactly where the flow restrictor is? in the joint of the rear right hand side pipe (cold flow into heat ex box)? i'm not too sure from the previous replies.

    Also i've got high cold water pressure if the restrictor is taken off do i then control the inbound cold pressure with the flow value?

    Ta
     
  15. jsstevenson

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    Hello...
    You have to take the front panel facia off of the boiler then on the right hand side of the boiler there are two pipes that bend into the side of the boiler - the one at the back is the cold water supply to the boiler - undo the compression nut (ensuring the cold water is isolated) and remove the fitting inside the side of the boiler that the pipe you have just disconnected connects to, then reconnect ensuring you replace the washer to ensure a water tight fit!!!!! You should then have DHW at a good pressure. So, yes it is in the rear right hand side connection as you said!

    As to your second question, yes you do control the inbound water pressure from flow valve.

    Good luck.

    Jamie.
     

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