My system was plumbed up just about a year ago and includes an anti-scald valve for the DHW as it exits my passive storage tank. A week ago, I went to bed with the tank temp up to 170 for the first time in a while, and was woken the next morning by my wife claiming there was no hot water for her shower, which was a bit of a shocker. I discovered that the ASV was only letting lukewarm water through despite plenty of hot water in the tank and in the DHW line leading to the valve. I took it apart, flushed it, and things were all good again. This morning the scenario repeated itself, including the fact that I had a really good charge of heat last night. My initial thoughts last week were that some crud had entered the valve and I flushed it out, but now I'm not so sure. Is it possible to develop an air lock, or is it likely that the additional excursion caused by hotter than normal temps is leading to a stuck valve? More importantly, what can I do other than replacing the valve, as it's practically a brand new piece in terms of its expected life?