weird grinding/howling/airplane boiler noise, appears only when Hot Water is demanded..NOT kettling!

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Hi all,

as perhaps this is my 100th post about something related to out kitchen renovation, I won't start this post by saying "we are doing a kitchen renovation..."

Our Vokera EasiHeat Plus25C, a three or four years old combi boiler, has been temporarily decommissioned (three months) meanwhile building work was ongoing.
At the end of January it has then been re-installed by an engineer. All checks have been done and the readings were normal, if not better than before decommissioning the boiler.

Since when it has been installed by the engineer, I had to flush the system twice as I had to install the kitchen rads that the missus struggled in finding its ideal choices of rads!
I have added inhibitor in the system.

Since a week or two, the boiler is making strange and daunting noises.
They are not kettling.
The way I will describe them now is perhaps as ridiculous as the way that wine connoisseur describe wines, however cannot find of any better ways!
Some sort of howling, or an old man whispering his last words before passing away after having smoked for the best part of 70 years; some sort of weird airplane / drone taking off or an interesting engineering contraption which hasn't been moved since the first world war and has all of its cogs and bearings well rusty and are grinding with each other.

Now, for the when do I hear this noise: I do not hear when CH kicks off, it is only to be heard when a demand for DHW is made.
It starts briefly after any hot water tap is opened in the house and, from the moment the tap is opened, the sequence goes: tick-tick (gas flame being ignited I assume?), then some sort of humming which is the most well known noise our boiler has made in the years (I assume the fans kicking in?) then as soon as the water from the tap starts getting milder in temperature, the weird noises described in the paragraph above kick in. They last for somewhere between half a minute and a minute and then they stop.
We do not have any problem with the water supply, we get it when we want it for how long we want it.

Today, after reading the boiler manual, I released the bleed screw on top of the heat exchanger, as the manual was saying to do so after everytime the system has been drained or refilled. Nothing has changed.

Short of calling the gasman around, is there anything else that I can do that can fix the problem? Is it a threat at all, or is it just a sign of age and I shouldn't be worried at all?

Thanks, much appreciated.
 
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When you open the tap, check if there are any other taps dripping/running?
 
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I f it was a tap or toilet valve I would expect to hear a moaning or shuddering.as the previous post said, turn on any hot tap until the noise is heard. Check all other taps while it's doing it. If you see any other hot tap dripping or dribbling there is your culprit. If none others drip its probable the one you turned on initially is the noisy one.
 
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Thanks for the advises.

@terryplumb getting the engineer back it is not an option I am afraid, unless I want to dash out some more money, which at this moment I rather not

@The Novice there is no other taps dripping / running when any one tap is open or when all the taps are closed; I don't understand what you are hinting at, surely the boiler is not expected to do abnormal noises if there are mroe than one tap in the house demanding hot water?

@duffin As per reply to the Novice, I don't understand why a second dribbling tap would push the boiler to make weird noises?

To clarify, the noise happens when any hot water tap in the house is open and no tap is dribbling.

To add to the "issue": I was aware there was still a bit of air left in the radiators since when the system has been refilled back a month or two ago.
I have now expelled air three days in a row, from one specific radiator upstairs as every morning you could hear the bubbling up there.

The boiler has now quietened by a large degree and you can only faintly hear those weird noises when there is demand for hot water.
Really struggling to understand why air in the radiator system would have an impact on noise when hot water is demanded??
 
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