I had to redo a gas fire installed by Eastern Gas (as was).
It was in a fireplace and replaced a radiant gas fire.
They connected it to the restrictor on the hearth, and it
worked OK whilst they were there. Some time later, I found
that after a long time, it would trip off. The cause was
that when the main burner lit, the gas pressure dropped
and the pilot light was very marginal on the thermocouple.
(It predates oxygen depletion sensors, or that would be
the first suspicion). Anyway, the cause was that there was
too much thin (gaslamp) pipework en route, reducing the gas
pressure. Eventually I replaced the gas pipe from the meter
for other reasons (disconnecting the gaslamp pipework) and
it got a new feed from the new pipework, and worked fine.

At 6kW input, and now being only decorative (originally it
was that room's heating but I subsequently installed central
heating), I can't really afford to turn it on anymore - the
boiler modulated down to 7.5kW can heat the whole house!

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]