I hope you brainy guys and gals out there can help me with this one. Our 3-way motorised valve (Honeywell V4073A-1039) sometimes doesn't go to the mid position (CH + HW), which means that occasionally we have no hot water in the morning, only heating. If I give it a light smack it then moves to the correct position and the water heats up. I've checked that the rotor arm of the valve itself is free - I can turn it easily in both directions with pliers, and the mechanism of the motorised valve itself is all moving freely. What could be causing it to stick in one position? The fact that it's intermittent (it usually works fine) suggests that all the wires are delivering the correct voltages, but I haven't checked. I tried setting the HW to "on all day" but this resulted in the CH sometimes staying on all day too - in other words, it was sticking in mid-position. It's quite a new unit (< 2 years) so I'm a little unwilling to shell out another sixty quid for a replacement. I have read the account on your excellent site at //www.diynot.com/forums/viewtopic.php?t=8369 on how these valves work, and from all that I've read I understand that the mid-position is sometimes the one that plays up. Any thoughts would be gratefully received. 
