Boiler making slight humming sound after hot water turned on

diystarter7

Hello
One of our kids, they have a valiant Ecotec boiler about 12 years old they think. 
Last 2 weeks they've noted when hot water is turned on at sink, and bathroom their is a slight humming sound like a mobile
phone on a sofa/etc. It often stops within a minute of turning off the hot water. It does this with the heating on or off.
The nosie has not increased and most people would not have noted it.

I've looked up Google and if it was the pump that makes more of a rumbling sound and this increases over the days/weeks.

Any ideas, please?

Thanks

ThisIsWeird

No idea. But the pump would be running pretty much equally for both the CH and DHW, but this noise only occurs during DHW (combi?)?

I guess that main difference between operations when the DHW is fired up is that it tends to be 'full blast'! The fan, for example, will be running at or near full speed, so I wonder if it's a fan bearing on the way out?

Just re-read your post - the noise continues after the tap has been shut off? Does the rest of the boiler seem to shut down as expected after no longer providing DHW, but this noise continues after this? If so, I'm stumped.

There's also a motor in the diverter valve, but that usually just operates very briefly in order to move the valve to its required position and then stops - the boiler then fires up. So that shouldn't be running either, and - if it did - surely the diverter valve would keep cycling between DHW and CH?!

diystarter7

Thanks, what is DHW, please?

ThisIsWeird

Sorry - Domestic Hot Water.

SteveJW

ThisIsWeird said:

The fan, for example, will be running at or near full speed, so I wonder if it's a fan bearing on the way out?

Just re-read your post - the noise continues after the tap has been shut off? Does the rest of the boiler seem to shut down as expected after no longer providing DHW, but this noise continues after this? If so, I'm stumped.

The fan on my combi boiler continues to run for around 3 minutes after running hot water or the central heating turns off
It makes a humming / buzzing sound

diystarter7

Thanks, no need to be sorry, thanks
Re the bearing, the sound is like a mobile phone left on vibrate on a sofa and you are in another room and just about hear it. It is not a continuous sound therefore not the bearing as that would be a constant wind, I think

i appreciate you trying to help.

diystarter7

SteveJW said:

ThisIsWeird said:

The fan, for example, will be running at or near full speed, so I wonder if it's a fan bearing on the way out?

Just re-read your post - the noise continues after the tap has been shut off? Does the rest of the boiler seem to shut down as expected after no longer providing DHW, but this noise continues after this? If so, I'm stumped.

The fan on my combi boiler continues to run for around 3 minutes after running hot water or the central heating turns off
It makes a humming / buzzing sound

Thanks but its only for 30 to 60 seconds and never happened before

Re bearing noise, looked it up on google defienetly not that sound, thanks

https://www.youtube.com/watch?v=uh4nEXrx62c

ThisIsWeird

When the fan bearings failed on t'in-law's old (non-cond) GlowWorm, the sound was completely different again - a deeply-unpleasant screech and rattle, as the fan wound up and down.

If a fan begins to fail, it can produce a range of sounds, from the screech mentioned before, to a 'thrumm' as the bearing spindle vibrates in the slightly-loose/worn bearing. This is similar to cars - when a wheel bearing begins to fail, it can often be a low rumble/thrum rather than a higher-pitched sound.

But, it's all guesswork, and since the boiler is otherwise seemingly working ok, the usual answer is to let it be until it becomes more dramatic, and easier to diagnose! Or until BUFF or another plumber comes on here

When you stand beside the boiler as someone turns off the tap, how does it respond? The whoooshing sound during instant heating of the DHW will be the fan spooling up to max, and this should stop - spool down - pretty much instantly as the hot demanding tap is closed. If that's also true of yours - the whooosh clearly dies away very quickly - but the vib'ing-phone thrum continues for a good while after this, I'm now guessing it isn't the fan, so that typically leaves the pump or the diverter valve as the only other 'motorised' components that would do such a thing. But - that's just guesswork too...

Although your pump (if that is what it is) doesn't appear to make this noise when used for CH, they are quite different scenarios; for CH the pump is sending a large volume of water around the rad circuit, and for DHW, it's a very short circuit loop, possibly with the pump running at max speed.

diystarter7

@ThisIsWeird
Thanks - all noted and preparing for the eventual problem and as you have suggested, this too is my plan, ie let it get more noticeable and then call out the boiler people.

I've had it with cars in the past, taken them in too early and once it was a wheel bearing and another time a drop-link on cars - the mechanics did not note anything until revisits weeks afterwards.
Thanks for your time and help.

diystarter7

Update
Having discussed with my family, I will visit soon and we will remove the front cover to get a better idea if we can locate where the sound is coming from. May do this if/when noise gets worse to give us a better indication.
Thaks again for your time and good help, appreciated.

ThisIsWeird

Where you'll find it due to a vibrating front cover...