I too am a LL. If your 1.7% increase is £13.50 then your rent is about £795 which in my area would probably get a 2 bed house/flat.
From his perspective, if your LL has put in a new boiler, that could have cost between £1-2,000 with labour. And double glazing could be £6-7,000, both rough guesses. So he's spent nearly a year's rent which I would have said was not unreasonable.
But it's his property and if he doesn't maintain it then he will be the one to suffer, both because it risks driving you out as a tenant (and evidently one paying over the odds) and the repair will take longer, cost more and lose more rent when eventually being done. I would say that 2 months is a typical void period with little or no work to do, with repairs needed it will be longer.
You should check with your local agents what is available in your area, what size and condition, and use that either to help you decide to move, or as leverage to negotiate with the LL. If he really is asking over the market rate and won't back down, then you would be saving real money to move and you would quickly recover your moving costs and be quids in every month.
Surely moving out of your current place would release the deposit to be used on the next place? And if he hasn't done much maintenance then it will be hard for him to deduct very much that isn't just fair wear and tear.
Also I believe there is a new 4 week limit on the deposit under recent law changes. I don't see why you'd need 6 weeks rent up front either. I wonder if you are painting too bleak a picture of the costs of moving.