diagnosing a blocked radiator??

[Hedd_Jones]

Thanks Rick - so has anyone had success flushing stubborn crud out of a radiator with chemicals?
I read a long post about the chemicals used, but I don't think anyone described how bad their rad was to start, and whether it actually improved.... (fernox or Holts seemed to come out on top).
It's been backflushed (in position) with a hose, and the resulting effluent was pretty much clean (I really was expecting a brown sludge!)

Yes.
Depending upon the nature of the crud I've had success with Fernox DS40 or DS3. DS3 is basically industrial sized kettle descaler and DS40 an expensive acid based clean.
The other good option is warm, 50% diluted brick/patio cleaning acid. You need to be careful, of course, but bung up the bottom pipe, try it for a short time (5 mins) and tip the waste into a clean bucket for examination. Some crud will be hopefully be dissolved and some loosened.
You've got an unusable radiator. What's the worst that can happen?

c

Yup

Kill or cure. Viakal also works. It all depends where the blockage is, and the general condition of everything else.

The chemicals will dissolve the blockage in time, but they may also dissolve corrosion products that might be sealing your rad from leakage.

We tried neat brick acid on my Mates Aveling barford dumper (with Ford 8 engine). Made the rad into a colander. Oops. Nevertheless it was U/S as it was. It had scored the bores it had got that hot