In article , Des Higgins
writes
hmmmm .... thinks..... I have just had my system drained down recently and I
do not know if the guy used inhibitor or not. Short of trying to find him
again, is there any way to find out if he did use any (now that I write
that; that looks like a silly question) or can you just put more in?

If you drain a little from a radiator bleed vent it should have a dark straw
type colour and a noticeable smell, however if there was none in there at
all then that straw colour could be rust ;-).

The manufacturers used to recommend a test which was IIRC to draw off a
small amount from a radiator, just 20ml or so, then dilute it 10:1 with clean
water to make about half a cup full (200ml) drop in a clean steel nail &
leave for a week. If there is any trace of rust on the nail then drain, flush
(with just water) & refill with correct level of inhibitor.

I'd only suggest this if the system had been fully drained & refilled to check
whether there was either some or none in a system, if the system was
partially drained & then refilled but no further inhibitor added then there
may be enough to pass the test, but not enough to protect the system for
the next few years.

I'm sure you'll get the 'it's only 20quid so put some in anyway argument',
but if your tradesman was a reliable chap(ess) & added the right stuff, then
that's 20quid that you can spend elsewhere. On the other hand, any
doubts then drain & replace.

phew bit long that, sorry . . .
--
fred