Combi-boiler pressure keeps rising when cold

Discussion in 'Plumbing and Central Heating' started by TedTrippin, 18 Jun 2018.

  1. TedTrippin

    TedTrippin

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    Hi,

    I have a Worcester Bosch combi boiler. I'll update the thread with model when I get home. It's like the 24i except it has 2 dials for CH temp and HW temp.

    I noticed the pressure gauge was in the red. I went to check one of the rads which usually gets air. No air. I drained one of the rads to get the pressure down to 1.5. Before I went to bed the pressure was back up to 2. This morning it was about 2.5. I haven't been messing with the boiler and I haven't added more water in some months.

    Before I call out the plumber is there anything I can check to diagnose the issue?
     
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  3. John D v2.0

    John D v2.0

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    filling loop letting by (£10s fix) or hot water heat exchanger leaking (£hundreds)

    1 Make sure the filling loop is actually turned off on both taps, and unscrew the flexible hose (turn off the stopcock first if you're worried) Then you'll see if it's letting by.
    if not and it still increases, 2. For the dhw exchanger, turn off the cold water supply before the heat exchanger (boiler inlet) and see if it stops increasing. Open a hot tap and see if it drops slowly.
    Others may have quicker ideas to check.
     
  4. muggles

    muggles

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    Is your filling loop letting by? If not then your plate heat exchanger is probably knackered
     
  5. TedTrippin

    TedTrippin

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    Cheers for those ideas. Will have a go when I get home.

    Hope I can disconnect the filling loop, its one those "hard" ones that you need to stick the plastic key in.
     
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  6. dilalio

    dilalio

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    Then you can't! Turn off the main stopcock overnight and see if the pressure remains at set level... If it does then boiler needs a new internal filling loop or see if you can make this obsolete and fit an external filling loop.
     
  7. Madrab

    Madrab

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    If you turn the mains off then it's going to stay at the set level regardless of what's passing, given the boilers mains inlet serves both the loop and the PHE ;)

    OP, time to get someone in methinks
     
  8. dilalio

    dilalio

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    Just testing :notworthy:
     
  9. John D v2.0

    John D v2.0

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    True but If he leaves a tap open overnight, the pressure will drop off it's the dhw exchanger, If it's the loop it will stay the same
     
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  11. phredda1

    phredda1

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    If the key isn't in the filling loop how can it increase the pressure?
     
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  12. ollski

    ollski

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    If this is the cdi 24/28 then it's usually the plates hx pinholed
     
  13. TedTrippin

    TedTrippin

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    I've been googling, it looks similar to the 27cdi. Can't find the model number on the thing!!

    Anyway, I closed the main inlet and opened a hot water tap. The pressure went down. So guessing that's the heat exchanger done in.

    I've got a plumber coming tomorrow save me breaking anything.
     
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  14. John D v2.0

    John D v2.0

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    Good diagnostics, do let us know the final outcome!
     
  15. dilalio

    dilalio

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    Yep. Sounds like that's the culprit. (y)
     
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  16. TedTrippin

    TedTrippin

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    Yep, was the heat exchanger. Decided to get the plumber out instead of trying to fix myself. Turns out I have a Greenstar 30 si which looked way more fiddly than the CDi's I was youtubing.
     
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  17. DIYnot Local

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