Car advice needed please! Leaky tyre valve

[daaaaaa]

Noticed one of my tyres on my new car (had less than a month) seems to be losing pressure more quickly than the others.

Saw a trick online which suggested pouring soapy water over the tyre and if bubbles form at the valve then the valve is slowly leaking air

Now I’ve been driving on it for about two weeks and it doesn’t go down too quickly. It should be at 30PSI but it’s dropped to 23 maybe every 3 days, at which point I top it back up. Not enough to trigger the amber warning light for tyre pressure.

Anyone have a rough ballpark for how much does it cost to replace? Does it need a whole new tyre or just the valve replacing. Complete novice with cars I’ll be honest.
Thanks so much.

Take it to the garage.
It's a new valve, and ten or fifteen quid.

Google new tyres (the name of your) town and see what comes up, if you take it in someone will be able to have a look at what the issue is and give you a price for whatever you need, likely just a new valve.
Avoid Kwik fit, they used to be good years ago but these days they seem to oversell and add on. They’ll tell you you need a whole new wheel!

https://mycarneedsa.com/blog/why-do-my-tyres-keep-losing-pressure

I’ve had this a few times. My local tyre place only charged £10/£20-ish to repair it.

I’ve also had a slow leak from a nail in the tyre. Again, they can repair it for less than £20.

Take it back to where you bought it. It should be under warranty and they will fix it. You really don't mess around with tyres - it might be a leaky valve or it might be something that will cause a blow out.

A while ago I needed four new valves which cost about £80. So, £20 for one valve.

If your valve is the problem and tyre is in legal condition, then they'll just change the valve.

Doesn't usually take them long.

My valve issue was my metal caps had siezed fast onto the valves and couldn't come off. Only use plastic caps! 🙈

Bought it from CarShop. It is under 90 days of warranty (so within this) but it says brake pads and tyres etc are excluded. I wonder if they’d make an exception for this since it’s been doing it since I bought it?

What does your warranty say about the wheels themselves? Rims, valves, etc?

Tyres could just mean the actual rubber only or all the above us excluded.