John Guest Underfloor Heating

 My User Experience So Far
For 3 years (2 year warranty BTW) my underfloor heating had performed very well, with the eventual (Planned) addition to the system of another area of floor (still within the pack rated area/pipe length) the wheels really came off my trolley, although the pipes appeared to warm up, the floor never came up to temperature as it had before.
In consultation with my builders and JG tech support it was decided to add a new floor pack for the additional space leaving the old pack running just it's original area.
Imagine my surprise when the new area warmed up but the old area remained cool!

The long and the short of it is that after a couple of weeks of personal investigation and experimentation I managed to compare the behaviour of the two systems individually and together and worked out that the bypass (Blending) valve on the original system was part opening once the system warmed up despite being set to MAX, our floor requires full temperature flow and so didn't stay warm once the bypass valve opened.

Remove the small screw retaining the knob, remove knob, lever off plastic lump with pointer. (realise the builders should have done this on installation and put them back where you could clearly read the current setting!) Unscrew the big brass nut to remove the cover, catch all the water, fish out the actuator pin, rubber sleeve & "funny spoked tube thing" with the thermostatic element built into it.

After pointlessly testing the thermostatic unit in a pan of water on the stove and finding that it is jamming simply throw away the actuator pin and reassemble to keep the blending valve permanently as shut as it can be.

Note to self
For future installations buy a separate pump and Blending/Bypass valve (if valve is required) and spend the spare £150+ on a higher quality modern pump with Variable Setting for Constant Head or Constant Flow options with digital readout whilst setting then power consumption display while running plus automatic bleeding!