Negotiations post surveyor report

We went to view a house that was advertised for 335k. After some negotiation we managed to agree on a selling price of 300k. Now when it has been assessed by a surveyor we have been advised to request a further 15k reduction in the price. This due to some needed upgrading, nothing that has to be done right away but surely before too long. Upgrading of a few windows, heating, plumbing and electricity.
The EA has told us the seller is very proud of his house and does not view the issues as anything worth a further discount as he puts it.
How do other posters view this? The surveyor is also doing the valuation report and he claims he can not value the house at a higher price than 285k. Any tips of tactics thats been proven useful are welcomed.

You might be on a sticky wicket if the 285k valuation report is for the bank. Are you getting a mortgage? The bank will only lend the appropriate %age based on the valuer's report, not the sale price. That's your main argument IMO & one the vendor may listen to.

My view is that it would be easy to see if windows need replacing just by your own viewing. Heating, plumbing and electrics are not so obvious but it may have reasonably been clear to you by e.g. the age of the house that you should have been aware that they needed upgrading prior to the survey. If that's the case, I can sort of understand why the vendor is being sticky about it, particularly seeing you negotiated a reduced price from the outset (it's just human nature - the vendor may think they have given as much as they can/want)

If the matters (or the extent of them) brought up in the survey are a surprise to you, then it's easier to argue for a reduction in price. If you can also provide the vendor with an estimate of what it would cost to replace/upgrade and the timeline you have been advised to do it in, that will also bolster your case.

I think your biggest issue is your mortgage approval, so I'd look at that as soon as you can.

If the seller doesn't want to sell for what you want to buy it (=what you think it is worth) then walk away. You have a professional opinion that the state of the house should result in a 15K reduction.
You can either ignore this and pay 15K more than advised or tell the seller that 285K is your offer. If he doesn't like it then I am sure he will find someone else to pay more, and wish him good luck with that.