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Baxi Solo 3 50 PF > Loud thump when starting from cold?

Discussion in 'Plumbing and Central Heating' started by Skyhigh, 26 Jan 2016.

  1. Skyhigh

    Skyhigh

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    Hi,

    I'd really appreciate any help so I can try to understand what this issue could be better.

    I've read around a lot online but can't find anyone describing a similar issue.

    When the boiler starts from cold, there's a large 'thump' from one of the pipes near the boiler (or that's what it sounds like). It literally sounds as if someone has hit a pipe near the boiler with a rubber mallet.

    The boiler is a Baxi Solo 3 50 PF, we have a 3-way Honeywell zone-valve and the system is open-vented into a header tank in the loft.

    Nothing has changed on the system bar having a Drayon 3-port valve changed for a Honeywell. This only really started about 4-6 weeks after though, so it seems unrelated.

    There are no unusual lights showing on the boiler (e.g. overheat, etc). It's turned up relatively high (and I've tried turning it down too).

    I've listed the potential points I've looked at below, although none seem obvious culprits (?)

    Ignition?
    I wouldn't call it a 'thud' or 'boom' or anything that makes it sound like the boiler is slow firing.
    It also only happens when the boiler has been left to go cold (e.g. overnight).
    There's no smell of gas inside or from the flue.
    I've yet to see if there's anything from the flue outside when this happens.
    (I may set the boiler to come on later in the morning after we get up at 6 to try and catch it).

    Kettling / Limescale?
    Although it didn't sounds like kettling, since the house was 15 years old and I wasn't sure how often inhibitor had been used (it seemed so), over Christmas I gave it a clear:
    - Drained down, cleaned header tank (joy), and refilled, added F3 for a week, let it run.
    - Drained down, refilled, ran water from each lower rad until clear, added F3 to run for a few hours, drained, refilled, ran water from each lower rad until clear, put in F1.
    - Each time refilled made sure there were no air locks and all rads bled regularly until all air out.

    To be fair, the water was pretty clear (slight tinge) and there was minimal amount of black sludge. The header tank only had about 1mm of black/particles. No foam in the tank or slurry, etc, even with F3 running.

    There is no gurgling / sucking / whoosing noises from the pipes/rads.


    Running Dry?
    I've read sometimes this can be a lack of water in the boiler, often due to a blockage, such as at the water-inlet (from tank to CH system). The header tank fills the system fine. Also when letting water from a drain-down point, it also fills the system fine.


    Low Pressure?
    Pressure in the rads seem fine. System is balanced and I've re-balanced it a few times to see if it makes a difference. The header tank is in the loft and all rads/parts of the system are below it. Draining from a radiator gives good pressure. All rads get hot.


    Air in System?
    I'm aware that air in the boiler & pipes can cause the boiler to build pressure & force the air/blockage - which could be likely. That said, there's no air coming from any of the rads, all rads get hot.
    Also, this only happens when the boiler is cold - so maybe something is 'settling'/'collecting' over time? (air, slurry?)
    When the 3-port valve was replaced, he didn't drain down (according to my wife), but used the isolating valves. That said, I guess *some* air could have got in, but the 3 subsequent drain-downs I've done should have surely shifted any locks..
    (again, there's just the thud - no gurgling/bubbling/rushing/sloshing in any rads to suggest air being shunted about)

    Blocked Flue or Vent/Outlet
    There's a lot online about a blocked, obstructed or iced-up flue causing loud noises on boilder start up. Flue looks fine.
    The boiler is on an external wall and vents directly outside through the wall (so flue is likely only 8-12 inches long)

    Aggressive Zone Valve
    I thought it could be the new zone vale closing/opening quicker/better - as the drayton was slow (first rad would heat up on call for hot water) and would stick in position.
    As this sounds near the boiler and only happens when it's cold - I think this is unlikely.
    Throughout the day when its coming on/off and the valve will be opening/closing a number of times, it's all fine.


    Worn Part / Failure
    Some form of part on it's way out? But why would any part function better when warm?
    (aside, maybe the ignition. But heating != spark and I'd suspect not any more helpful to helping the boiler light)



    Any comments/suggestions appreciated!

    (FYI - I'm booking someone to service the boiler and take a look as I won't touch gas appliances, but still want to try and route out the issue as, like most, I'm interested in how things work - and so far, I can't seem to pin this on down.).




    Cheers,
     
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  3. Agile

    Agile

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    Makes me wonder if the motor valve has been put in backwards!

    Unlikely to be anything in the boiler.

    But you could turn off boiler on its own switch and select different combinations of CH and HW and see if it still makes the noise.

    Tony
     
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  4. Skyhigh

    Skyhigh

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    I'll turn the boiler off and put a call on for CH then HW separately to see if I can replicate the issue.

    I'm pretty certain the valve is on the right way (and wired correctly) - I checked the pipes for each (i.e. CH feed was hot when CH was called for and the same for HW) after he installed it.
    CH and HW come on correctly when called for too.

    Looking at the Honeywell 3-port instructions, it's also installed/sited correctly as per instructions (e.g. it's no upside down or incorrectly orientated).

    Unless you mean something else maybe?




    Cheers,
     
  5. 45yearsagasman

    45yearsagasman

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    My money is on the Honeywell 3 port returning to hw position with a thump. Those valves are not as good as they once were. Changed a couple recently for friends.
     
    Last edited: 27 Jan 2016
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  6. Echo the husky

    Echo the husky

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    Me too, the mechanisms just seem to fall apart on some of the new ones, and are often faulty before they have even been fitted. The teeth seem to jump as if they are bady worn or poorly aligned.
     
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  7. Agile

    Agile

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    Back to basics, is the pump on the boiler flow or return?

    Tony
     
  8. DP

    DP

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    My money on the valve also.

    Replace the valve with one that has paddles in it instead of ball and lever
     
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  9. jeff the gasman

    jeff the gasman

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    Mine is also
     
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  11. Skyhigh

    Skyhigh

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    Money well placed, it's the 3-port valve.

    Oddly, I've opened the valves on some rads up and it's got a bit quieter - I'm assuming this has dropped the pressure on the main CH loop. I'm also sure that it wasn't noisy when installed by the engineer only 2 months ago. That said, I've probably noticed it over the past 5 weeks.

    Looking online it's a mixture of "Honeywells are noisy" and "if it's new, it's a bad batch".

    What are you views on where I stand with the fitter?

    I'm aware it's not his fault, but to be frank I don't want to pay £100 for another and then £75 for him to fit it again.

    (I know I could buy the valve myself for £75 and replace the motorised head, assuming it's that and not the actual brass valve/spigot itself that's sticking.)



    Cheers,
     
  12. Echo the husky

    Echo the husky

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    Call the fitter and explain. Where I work we would replace it completely free of charge if it's under 1 year old.
     
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  13. Agile

    Agile

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    What has happened for you to now be so sure that its the valve at fault?

    Many of us here think that it probably is but none of us have been there.

    My view is that you should just call the installer.

    I have to say that if the valve is faulty or just noisy then the installer should change it at no further cost. I certainly would!

    Tony
     
  14. Skyhigh

    Skyhigh

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    Just coming back to this - when switching between hw/ch (boiler offer) the valve does make a 'thud' sound which can also be felt if I have my hand on the motorised valve unit itself or pipes that directly connect.

    I'll be calling the guy who installed it out to take a look.



    Cheers,
     
  15. sooey

    sooey

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    Did you buy the valve and pay him to fit it or did he supply and fit?
     
  16. Skyhigh

    Skyhigh

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    He did the supply and fit, in fact he recommended the Honeywell to replace the Drayton that had failed.

    (tbh, I could have bought the a little valve cheaper online myself but just wanted it sorted)


    Cheers,
     
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