Warranty claims and online stores. Who pays for postage?

I have an item with a 2-year warranty which needs a repair after less than a year. The online store in question has asked me to send back for a repair under warranty. I'm happy with this. But they're telling me that I have to pay postage.
Is this legal? Surely if it's a warranty job then I shouldn't be out of pocket. ie: they've sold me something that doesn't work so the repair comes at their cost, not mine?
Not prepared to name and shame, generally their service is very good.

Are you having it repaired under warranty – which is supplied by the manufacturer and is discretionary or using your rights under the sale of goods act / distance selling regs?

In the first case they can set what conditions they like, in the second they retailer pays the postage

Warranty. I just looked thru distance selling regs and couldn't find anything re cost of carriage for warranty returns.
What I don't get is they say they pay postage if return is within 6 months, which is totally arbitrary

They pay for return postage: http://www.oft.gov.uk/NR/rdonlyres/1E6F3C94-8BB0-4374-A65B-6281E030C3C9/0/oft698.pdf

Arbitrary or not – they are offering something above the basic legal rights so can set what conditions they want.
Your rights under distance selling and SOGA are the legal minimums – anything more is discretionary.

What I don't get is they say they pay postage if return is within 6 months, which is totally arbitrary

3.68 If goods develop a fault within the first six months of being sold,
the law presumes that the fault was there when you sold the goods –
unless you can show otherwise. You should not charge return costs
for goods that have been rejected because they are faulty.

They should still pay postage for warranty returns.

Bike shops have always had to pay postage on items they send back to the distributer for warranty issues.

……….in the main
………….as far as I know

Bike shops have always had to pay postage on items they send back to the distributer for warranty issues.

That's B2B and doesn't come under the same regs.

I've just sent a helmet cam back to the US for warranty repair. I paid. I did buy it from a UK store but didn't want to run the risk of getting another with the same fault, and after talking to the manufacturer agreed to send it back.

I also paid VAT on the return leg because they didn't fill in the forms properly according HMRC. I could try to claim it back – but the process looks like a nightmare. So easy to take, so hard to get back 👿