I had problems in mothers house, the hysteresis was huge, the valve did work, but when it called for heat it over shot the mark by a good margin. I had electronic heads, so they reported both target and current in °C so easy to see some thing wrong.
I tried different spacers, and pound coins on the pin, non seemed to work, then I tried adjusting the lock shield valve, and as I closed it the over shoot reduced, so set at 20°C I closed the lock shield until over shoot just reached 21°C, and I repeated for other three heads, there seemed to be no problem hitting 20°C even on very cold days, so I closed just a tad more.
From that point all the four radiators with electronic heads were spot on the setting, so I removed one head and fitted it to all other radiators in the house, adjusting the lock shield valve until target and current matched, then replaced with original wax head, once the lock shield was set, the standard wax head kept the temperature very close to setting around half way 3 to 4 gave me 20°C.
After the event the reason was easy to see, with the TRV on the return the radiator gets stinking hot before the heat reaches the head. The cheap eQ-3 electronic head has 4 error codes, first is battery symbol which shows battery needs changing, but the other 3 are really handy working out when a valve is faulty, F1 valve drive sluggish so warning it's starting to stick, F2 actuating range too wide, likely not screwed home on valve, and F3 adjustment range too small likely valve has sized solid.
With a °C setting so no guess work, it is so easy, I fitted blue tooth version at £15 each, the non bluetooth found at £10 each, at that price why fit wax? I have bedroom temperatures set so radiator not running in the day. I have 9 brand new never used wax heads, never likely to be used. OK those I brought from mothers house were far more expensive at around £45 each, the cheap ones only show target they don't show current.
However the point is likely it needs lock shield adjusting with the wax or liquid heads you have no idea if working or not, with the electronic you can hear them adjusting, no loud, but you know they are working, and you also know if jammed with cheap ones, oddly the expensive do not tell you if jammed or if reached end of travel, in many ways the cheap ones work better.