Myson MPE322 spring return issue

[Plummbob]

Hi

My actuator is getting stuck on in the central heating position. This seems to happen when there is a demand for water heating at the same time - eventually the house warms up, the water never gets heated (as all the flow is to the central heating circuit) and so the central heating thermostat clicks off - but the pump keeps running as the hot water thermostat is never satisfied (or maybe the pump keeps running coz the actuator is turning it on as it’s stuck).
Now the odd bit - if I touch the actuator very gently, the tiniest of nudges, you hear it snap back into the default position due to the return spring - and we are all good until it happens again. The actuator is pretty new. I’ve loosed the screws holding the actuator to the 3-way value plate, in case it was a slight alignment issue and it was jamming/failing to turn the value. This made no difference. The valve is definitely hard to turn - I can turn it by hand with pliers but not just with my fingers.
So - are the values normally that stiff? And is that the likely cause of my issue (not something I want to replace in a COVID19 lockdown scenario!), or a faulty actuator?

 

[CBW]

Sounds iffy, but maybe check for alignment? How new is new? I have customers tell me “that boilers only a few years old” I find it funny when I say “it’s about 12 years old”.

 

[Plummbob]

The new actuator was fitted about a year ago, as part of trying to diagnose this problem. I've caught it on video, you can hear it click when it snaps back after the slightest touch - see https://www.dropbox.com/s/u1kzimfjga0dn7s/Actuator.MOV?dl=0