I always encourage anonymous people on the internet to work on electrics.
Aaaaaaaaand guess what? Everyone is telling you the same thing: to replace the valve head. Please use your "skill set" which you are sure you have. If not, follow Offgridman's advice
And don't touch anything or do anything that you are not competent to touch.
There. This supercilious chocolate tea pot has just repeated the same message twice.
Ps. Apparently 2 people found my comment amusing
Thank you for your considered response. As I am sure you must have read my first post
. You will have noticed that I didn’t ask how to replace the valve head, just whether the “ticking” was normal? If not, how to test it, although I believed, subject to confirmation, that I had figured out how to test it! You have not answered, or confirmed whether it can be tested easily or not, but as others have stated, it still seems to be working, albeit with this noise.
You would not have known that I have been a cable manufacturer/ installer for 45 odd years, so understand electrics fairly well although am not, nor have ever needed to be part P certified.
You would also not have known that we have insurance that covers this part and the replacement therof, but as I was only asking if it could be easily tested, this information was superfluous.
Your statement about not having the skill was an interesting one as, without knowing a test method, neither you, nor I, could judge whether I had the required skill level, or not.
As it appears from the above comments that it should be replaced, I will call out HomeCare and ask them to replace it, however I cannot say that I am confident of their “skill level” either, as they have, in the past, forgotten to solder up solder joints.