No idea, I think I’d better have a word . TBH I haven’t had a single tradesman at my house (it was a bungalow and is now a house) who hasn’t cocked something up. I’ve found that often it’s easier to sort things out myself. I’ve got an Infra-red thermometer. I can have a go at balancing the system myself. What temperature difference should I be looking for?
I’ve turned off the second pump and checked the boiler pump setting it was on the highest constant pressure setting (4) so I have changed it to variable (0). The rad that didn’t seem to get hot without the 2nd pump is now heating up. Have I done the right thing?
Didn't see this bit until after writing my reply above.
There's nothing wrong with your solution.
The fact that setting the pump to variable solves your problem shows that the circuit resistance is high. This is probably because the installer balanced the system for a low temperature difference (10C). This is OK for an old boiler with low resistance cast iron heat exchanger, but not for a modern condensing boiler which has a high resistance ali or stainless steel exchanger, designed for a 20C difference. The higher difference means that the flow rate is halved and the resistance of the complete system is reduced by a factor of 4. The pump therefore has much less work to do.
Checking how far the lockshield valves are open will tell you if the installer has correctly balanced the system. Remove cap (undo screw and pull off); turn spindle clockwise, counting the turns, until it stops; return to original setting. If you have to turn the valves more than one to 1½ turns the system has not been balanced properly.
How many motorized valves do you have? If there are two, you need an automatic bypass valve.
Balancing. The actual temperature difference is not important, but you need to aim for a temperature difference no greater than 20C. This will normally mean that lockshield valves are open between 1/4 and one turn. Start with them all at 1/2 turn open. Make sure you remove all TRV heads while balancing. make very small changes (1/12th to 1/6th turn), one rad at a time and wait five minutes before checking. Closing the LS valve increases the differential and vice versa. A difference of a few degrees between rads is acceptable.
Yes, IR thermometers are influenced by the surface they are pointing at, but if all your pipes are painted the error will be minimal. Bare copper pipe (e.g at boiler) needs to be wrapped in some insulating tape (any colour) and the reading taken off the tape. Hold the IR thermometer against the pipe so it does not pick up background heat. (An IR thermometer collects over a conical area, like the beam of a torch.)
you would be better to have the second pump removed and a straight section of pipe placed where it was, the pump will cause a restriction, not necessarily a huge one but could cause problems later on in the systems life.