Hi Guys,
Just thought I would update you all on how I have been getting on with this strange problem. Something funny happened yesterday!
Yesterday, I intended to replace the MV. But first I took the pump head off to see if its got any crud in it - it didnt, it was totally clean.
Then I took the MV actuator off, incidentally, I turned the valve with my fingers (this time with the power off of course due to disconnected pump) When I did this it did not move freely like it did before - if flicked from left to right with a far amount of force, and made a pretty loud clunk noise whenever I did it, which was a few times. Last time I did this (with power on) the valve spindle moved freely with no clunking, and I could move it wherever I wanted (eg in the middle), without it clunking straight to one side or the other.
Impiortantly one thing thing i noticed, once the actuaator was loose - it rattled badly - there was something inside it loose, and something not too small too, which really tattled about when you shook the actuator. Im thinking now whatever was rattling loose inside the actuator was impeding it from working properly.
Then I went down the plumbers merchant for a new actuator (Drayton MA1 3 port). Well it was well too pricey! I seen on online for much much less, I figured it would be more down the merchants, but not like double the price. So in the end, I left it, and came home and put the old actuator back on. (I had not removed any wiring).
So heres the funny bit - after this (effectively doing nothing, just removing existing parts, and put same parts back) it seems to be working fine! You may remember I caan recreate this problem now by doing a specific sequence of events, I tried many times yesterday to get it to trip out (its not 100% that it does it everytime) but I did not trip out once! 10-15 times, nothing. Although in the yest morning before I did the above, I tried it once and bang - 1st time it tripped out.
How strange! So basically, I do not think disconnecting the pump was anything to do with it, I think taking the MV off and getting this clunking noise on the valve (or much more likely - the loose thing rattling inside the actuator) has somehow cured itself, and now, fingers crossed it seems to be working fine!
Best bet is that, by me shaking the actuator made the loose part rattling move to a different, non problematic area in the actuator, out of the way so now it works good again. Just a guess, I'm no expert, seems to be the most sensible guess though.
Thought I would let you all know, maybe someone else may have this strange problem, or one of you will in the future. Thanks very much for all your help, its been much appreciated. Im pretty hopeful it will all keep on working OK now, if not seems clear enough just to replace actuator. Thanks all once again.