How difficult are the plate-based wort chiilers to clean? Do they require filtration before the wort goes through them?

If you have a stainless steel plate chiller, don't store acid based sanitizers (such as Starsan) as they will eat up the metal. I've been using a Therminator for just over 10 years now, well over 100 batches...and have never had a problem. There is a video online of a guy cutting one open that he had used for several years and there was nothing in there. Nothing. You have to take care of it, obviously. I clean mine within 15 minutes of every use. I used the Blichmann backflush hose hooked up to my sink and flush it with hot water for 2-3 minutes in each direction...I do this for a total of six times...three times in the forward flow and three times in the backward flow directions, alternating between each. I then submerge the therminator in a kettle of water had keep it at a boil for 30 minutes. I then drain it in the sink and tip it back and forth on and off over the period of three days until no water is coming out upon tipping it. Then it goes back on the shelf until the next brew day.

I've seen pros store sanitizer in the plate chiller, just pump it in and cap it. Then when you push wort through, you simply wait for it to push the sanitizer out, as far as gross debris, PBW and some Really hot water does the trick for everything else.

Unless you're careful with filtering, plate chillers can and do clog up with debris. Any debris that's trapped during transfer needs to be backflushed out by connecting the wort inlet to the water supply. The high pressure usually pushes out most of the debris, but it's still necessary to bake the chiller in the oven every few batches, and maybe run caustic soda through it once a year to clean out any resident crud.

Here's a pic of an unused shirron plate chiller cut open

The amount of gunk trapped is usually it's not enough to significantly stop the flow, but I've had flow trickle to next to nothing on more than a few batches. For example, I recently tried whirpooling through the plate chiller, and flow ground to a tiny trickle after a few minutes. I was using hop-bags, but still hop pellets and trub can make it into the chiller.

A hopback makes a great filter and pretty much stops any trub from reaching the chiller. You can build your own from a canning jar, or buy them ready made for about $125.

I'm scaling up to 10 gallon batches and looking to buy a new chiller. I will pass on plate chillers this time round.

Also from the same thread:

I also pump a lot of water through mine after every brew and blow it out with compressed air (with inline oil filter). Then the day before each brew day I countercirculate caustic beer line cleaning solution with a pump designed for beer line cleaning. The output from the chiller (normally the input) dumps into a bucket and the pump sucks up solution from that bucket through a fine stainless steel strainer. At the end of a few minutes of this the solution has turned dark and the strainer is covered with material. After an hour of circulation the solution is much darker and the strainer has a remarkable amount of crud on it. IOW, there is still plenty of material left in the chiller and it's not soluble even in caustic (the crud on the screen does not dissolve). It's probably bits of hops petals that made their way into the system. I have to disassemble the thing one day and clean it properly but it's not a job I'm looking forward to. No infections so far (touch wood) so I guess my protocol has been successful thus far, at least.

Brad Smith had John Blichmann on the BeerSmith podcast recently and they discussed cleaning and sanitizing these things. Seems like a non-issue to me after hearing John describe it. You just back-flush with hot water, then PBW, then Star-San and call it a day. Do it immediately after using it to prevent crud from building up. Those I know who have therminators have had no issues with keeping them clean nor have they experienced any infections.