Something like this, I wouldn't spend more than £15 or £20, all you want to monitor is the pump power in watts, nothing fancy required.
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Don't know where you live but you can get one of these in Maplins? or the like, or Amazon.
For initial pump test, (boiler off) just note and remove the terminal numbers where the pump cable is connected, then remove it and fit a 3 pin plug to this cable, then plug the energy monitor into a extension lead powerd from anywhere and plug the pump lead (with now 3 pin plug) into the power meter and you can carry out cold pump tests with boiler switched as the 3 way valve will allways be open to either the CH or the HW. Depending on results, to do a longer/hot test, get a 3 pin socket and connect it with a bit of cable, connect the other end into the terminals where you removed the pump cable, then connect energy monitor and pump cable as above and fire up your boiler, you can then monitor the power indefinite