Any boiler experts around? Loud buzzing noise

[BabCNesbitt]

We've got a Vaillant Ecotec Pro 28 boiler in the house we rent. For a little while it's been making a bit of a scraping, clunking noise when the heating switches on, but it usually stops pretty quickly. This afternoon, though, when I put it on to comfort mode, it made the clunking noise then started buzzing like an angry hornet with a megaphone was trapped inside. The radiators are still heating up, though.

If I switch the heat off again, it keeps buzzing and an hourglass flashes in the small display. After five or ten minutes, the hourglass finally disappears and the noise stops.

Any ideas? If it carries on, I can call the landlady, but I've had to contact her 2 or 3 times about this bloody boiler this year and I'm reluctant to bother her if it's not essential.

turn it to eco mode, see what happens.

I think it will be an electrical moving part, such as the diverter, that is trying to operate but is jammed or is not closing the contact after moving. I think it will need professional repair so you ought to contact the owner. Winter is coming so get it dealt with before it is an emergency.

Thanks for replying, PigletJohn. Funnily enough, after I ran the upstairs hot tap, the noise stopped and hasn't restarted - would you still recommend that I get it checked, even if the noise doesn't come back?

yes.

could still be the diverter

When was it last serviced?

Um - fairly recently, I think. Within the last year. It's had various issues with blocked filters and so on.

Hi. Can I ask whether, and how this wss solved. Our boiler has been buzzing on & off for a few montgs, but now its more often. Hope yours is ok now...