I have a shower with a thermostatic mixer valve that is fed off a combi boiler. When it is working properly, it can get very hot. Intermittently - for a period of a few days to a week - it only gets to a temperature that is best described as on the cold side of tepid. The pressure is unaffected. The problem is not related to use of water elsewhere in the house.
I'm wondering whether this could be caused by limescale somewhere in the shower mixer causing something to stick and what can be done about it. We do get bits of limescale showing on the shower head, but it's not blocked.