Thanks for the replies folks a lot of good information there. I appreciate you all taking the time.
I have found the IR thermometer to be reasonably accurate, but you do need some tape on the pipes to get an accurate reading and it is fiddly – wouldn’t want to do it regularly with this. Based on the known temp coming out of the boiler and checking the readings on the pipe there I am confident that the readings are close enough for this purpose.
I have balanced the whole system now, took ages with so many rads but the with all the TRV’s fully open and the system up to temp the last two rads were fairly close to fully hot with the their lock valves fully open. From this I don’t think that the boiler is over or undersized, I think its probably fairly close. Even if it is slightly undersized I don’t usually have any more than half the rads on at one time anyway. I also checked the differential at the boiler and its almost exactly 20 deg.
I had went through the boiler sizing exercise before I got the boiler fitted as different heating engineers were recommending greatly varying sizes and I was getting something between 28 and 32kW. This boiler I believe has 32kW available to the heating system. I also thought that given 20 radiators and approx. 1.5 kW from each that this was an approximate match too. Its difficult to make any assumptions about the output of the rads as some are fairly old without the convecting fins and some are brand new.
When I checked the temps at the boiler I was getting 85 and 65 and although I believe this means that the system is balanced, I also understand from what I have learned here that this means that the boiler won’t be running in condensing mode so I have turned it back a bit and will check it tomorrow from cold and set to about 70 deg output for now – although I might need to turn the output back up again if we get a winter like last year, it was -18 deg here one day last year.
Hopefully that’s it, I presume that changing the boiler output temp wont affect the balancing but I will check all again tomorrow running up from cold.
It is a little frustrating having to do this after paying nearly £3k for a boiler to be fitted. I would have thought this reasonably good value if it was all done right first time. On the upside I do know a good bit more about my heating system than I did last week!!