My printer has been stable for weeks. Suddenly the first layer was WAY too close. Systematically. I knew previous print had come of easily and hadn't moved the bed. So first check was that the IR sensor was not catching on the dump bucket and being moved around. Not at all. Tried starting several prints to no avail. Then decided that perhaps the bed was a little grimy around the place where the sensor does the homing. Cleaned that patch of the bed. Then suddenly prints were starting WAY too FAR AWAY!! Little tubes of toothpaste. Hmm. So it did have something to do with the homing area? However still couldn't start a print and, having no desire to completely redo mesh levelling, tried putting down a milky thin layer of glue in the homing area. Restarted a print and first layer now 100% perfect just as it has been these past weeks. Is there a lesson in there somewhere? Have made a fool of myself before trying to explain what the IR sensor is thinking. So now will leave that to others. Would just like to add though that one of the many marvellous things about the sock is that you can stop and start prints willy nilly without having to keep checking to see what has oozed out of the nozzle and is now burning off on the heater block!