Andrew Gabriel wrote:

In article ,
"Mike" writes:

"Jeff" wrote in message
...
What's this about having to fit a bypass valve to comply with building
regs?
Can't I just leave one rad without TRVs or isn't that the same?

depends on configuration of your system - see below

....
That said, saying leaving just one rad sounds like you only have one
heating
zone which doesn't meet the building regs except in small flats. You
need at least two

reference?

This just isn't true. I've looked round a number of new houses
recently for a friend (3 and 4 bedroom), and I've never seen
one with more than one heating zone. Zoning the heating is
something really rather restricted to committed DIYers.

IIRC it's required for larger houses but I can't remember the size threshold
or what reg it's in (part L, I'd guess)


and each would need a rad without a TRV.

Yes, and you must ensure a water path remains after the call
for heat is gone during the pump run-on period.

thus a bypass is needed for an S-plan system but not Y-plan (where the 3-way
mid-position valve provides a path via the HW cylinder)