phenolic beer

So, I have just managed to brew my fourth phenolic beer in a row. Ouch.

It's the worst flavour fault you can possibly get. There's no calling it an esoteric design feature, no passing it off as an authentic quirk of a craft skill. Not even any saving it until everyone's already drunk and slipping it past the weary tastebuds.
It's the one that renders it completely undrinkable, the one you really do have to throw away.

I thought this problem had gone away after having about ten of them last summer, and then having a winter of good beers. I don't know what changed; I've been given suggestions, had changed a few practices; but still haven't pinpointed what exactly is causing this. Here are a few of the ideas thrown in so far:

Burning the grain.
I use my boiler as a mash tun too, with a grain bag. I used to stick the grain in the heated & treated water, and when it dropped below temp, fire it back up with the grain in. I don't do that any more. Now I unplug the thing before the grain goes in, just to make sure. So it's not that.

Mashing too hot
This came up on Jim's Beer Kit, but I vary rarely get the mash temp wrong, and have been through a few thermometers now, they can't all be incorrectly calibrated, surely, even if they are from wilkos.

Too much trub going through in to the boiler.

I hadn't really given this one much thought. I use a grain bag, so don't get lumps in the runoff to start with. But recycling the first few litres back through the grain until it runs clear, and skimming the boil, are definitely things I'll be doing in future just to make sure.

Fermenting too hot.
OK, so it was mainly a summer problem. I don't have temperature control as such, more a cupboard 'under the stairs' which tends not to go above about 22c all year round, which kind of just about does the job. I have brewed really great beer in the summer, and phenolic in winter, so I don't think that's the problem.

Insufficient sanitation.
Since the problem began, I've not only taken everything completely apart and bathed it in bruclean, I've also replaced eveything, at least once, even the boiler. So I really don't think it can be that.

Chalky build up in the fermenter.

Apparently this can harbour lots of nasties, and if it's a bacterial infection then here's one of the many places to look. But one thing I'm bloody good at is cleaning. Bizarrely, I don't mind it. I find it meditative. Hell, if it paid well I'd do it for a living. Almost. My boiler doesn't have chalk in it, and neither does my shiny glow in the dark kettle. So it's not that.

Bad bottle storage.
I used to sanitise them, rinse them, seal them and store them. I later realised that there is a risk of some of the bottles not being completely dry before storage. So I could have been pouring beer into a bottle with stagnant water in the bottom. Oops. So now I have a bottle tree. That won't happen again.

Insufficient rinsing of chlorine based sanitiser.
I thought I was doing ok. But now I'm rinsing with bruclean, then water, then sodium metabisulphite, then water. Short of killing them with fire, that surely covers it.

So, after all that stuff, I'm out of ideas. Hopefully I'm all cured and the ones in the conditioning cupboard will be phenol-free joys to behold. But, if my next few do the same... Well, I don't know where to go from here.