Thought I would provide an update on this one, as only fair given all the advise given to date. Currently running system with x400 sentinel in it before giving it a manual flush using mains pressure in a couple of weeks time.
What we found to date - 2 problem rads (slow to heat and not heating fully) off the wall and flushed outside, some muck but not excessive. £50 spent on new TRVs and lockshields on these rads and others, all to no avail. Flow and return both confirmed as not blocked and decent flow at rad (by removing rad and opening valve on the pipe tails). Rads confirmed as b-directional by manufacturer however interestingly swapping the TRV to be on the OUTLET of my son's rad did add 5-degrees to the rad temp (when rad was off I opened TRV and lockshield to see flowrate and was amazed at how much more flow through lockshield c.f TRV - originally on the oulet leg - gave). Thought, swapping them might be worth while and so it proved (gained 5-degrees) and of course checked the TRVs bi direction setting was set as outlet now.
I then re-balanced system with rads next to bioler closed even further from 1/2 - 1 turno open originally to 1/4 to 1/2 turn open now (tiny amount when you look inside one of the lockshields I replaced, but amazingly the rads still heated up quickly). These LOCKSHIELDS are nearly 5 turns to fully open! This also improved temps slightly. Slight worried the small aperture settings will furr up with gunk and so thinking about installing a magnaclean in due course or re-balancing with the pump speed at 2 to get increased aperture settings on the lockshields. Any thoughts?
Currently runnign the x400 more as precaution given 5 years old and only bought home 18m ago, but hopefully this plus a re-balancing of the system will address the issue (FOR MY SON AT LEAST). His rad is the last in the line upstairs. Unfortunately the front room rad (last in the line downstairs is still not great). Had reason to go under the floor for the 1st time since buying the home at the weekend and was surpirsed to see the downstairs rads are fed off a 22 manifold and all rund 10mm microbore!!!! U/stairs is all 15mm PVC.
All downstairs rads are fine except the front room, which is some 6m from the manifold on 10mmm microbore. The manifold feeding this rad is a JG Speedfit Inline Manifold 4 Port unit.
My Q is, would a 12 m loop, 6m there and back feeding a 1kw rad be OK on 10-mm microbore or shoudl I consider upgrading this pipe to 15mm to help get increased flow to this rad? The issue of getting heat to the rad has never been there - always high 60-s at inlet, just no flow through the rad so huge temp drop and little heat.
Before anyone says it, I know I could have got a GS engineer to look at this weeks ago, but this is now a point ot principal for me that I, with your help, will fix this!
Thanks as always for the feedback.