Sudden influx of flies! Please help

[stilllovingmysleep]

Hi, since yesterday we have had many black, sluggish (almost asleep) flies come into our house. We don't know where they are coming in for and why! Yes we had open windows and doors during day yesterday but then once we closed everything they were still coming in. At night we secured the downstairs areas by closing doors to try and identify where they're coming from and this morning there were still some in the kitchen! Where on earth are they coming in for and why when all windows are closed?! Please help with any ideas or experience, they're disgusting.

Just to add I think we've identified now that they're coming from inside the boiler. Maybe they were hibernating and have woken up now? But there's loads. Called pest control and will cost loads to fit in a fly catcher thing and fly traps. Wonder if there's other advice / ideas that won't cost loads?

A fly has laid eggs and the maggots have become flies. It's possible there a dead bird or mouse or something that got trapped near the boiler and they've come from that.

Thanks wowfudge. Advice on how long this may take until they die out or what to do? We initially thought its from the boiler but in fact they seem to be from a crack in the floor / wall. I called 3 pest control companies to advise me and it's shocking how different each ones 'a advice was!

Do you have a bin outside and have you checked it for maggots? Are the flies coming through an airbrick outside? If you have a airbrick/vent outside have a look to see if there are maggots there, possibly some food/rubbish has landed in it, in which case a bucket of bleachy water over that and then a load of fly spray in the room should do the trick, make sure to shut the doors after spraying and spray any surfaces you think they are coming through. I speak from disgusting experience here. They were easy to get rid of once we identified the source and we didn't have to pay anyone to help.

We've now identified they are coming through a crack on the floor at the kitchen entrance. DH just sprayed and lots came out half dead. Clearly something dead is in the wall there / under the floor. We can't smell anything though. Sadly the area where we sprayed has no door, opens into the halfway so can't prevent the spray going elsewhere.
Will open windows.

Probably a rodent under there, keep spraying as these flies will be young and dopey, can you fill in the crack? is it grouted tiles that you could repair?

May be cluster flies, they return to the same place each year, are large and dopey and noisy

They are smallish black flies and dopey / sleepy / easy to kill. We'll keep spraying yes...

What could the crack be filled in? We plastered / did floors in the autumn but that bit opening to kitchen wasn't done properly as the kitchen floor will be done in the future months so we didn't think it was worth doing now (hence the crack).