Velvet wrote:

However, with all the rads shut except the bathroom (and this wide
open), the boiler kettles. Same if I have the kitchen rad wide
(closest downstairs one to the boiler, and the only other candidate for
having the TRV disabled on it). So two wide, pump on min, kettles and
short cycles. Set pump to middle and it stops the kettling, though a
little short cycling going on, with periods where it's doing it right
(and modulating up and down in the longer burn cycle).


I wonder if the system is clogged up a bit and/or the high temp stat
isn't working or there isn't one fitted. You could modify the bypass
to avoid havign the microbore and maybe fitting and auto-valve would
mean that the super-hot feed water gets fed back into the boiler and
it'll then shut down rather than allowing the water to overheat.