Just noticed one of the TRVs leaking - from the pin. Tried various thumps,
twists and tightenings, but it's still weeping a little. In my spares box I've
got a number of TRVs that I've 'improved' over the years, but they have
different markings and part numbers.

They both have arrows in both directions, so bidirectional I'd guess. But they
have different part numbers (that resist google), are marked 'GB', and
different symbols. One looks like a comb (radiator?), and one looks like an
inverted 'U':

https://www.icloud.com/sharedalbum/#B0z5idkMwmb0Bb

Are they the same thing? They were fitted at the same time by a plumber who,
when fitting a new boiler, uprated the valves to comply with regs.

I'm going to try a quick swap without draining the system down - just emptying
the radiator and taking out as much pressure as I can. Wish me luck :-)

--
Cheers, Rob