Direct central heating system

[chasbo]

I'm changing a radiator to a towel rail in the loo. Unpacking the TR the instructions state ''Not suitable for a direct central heating system'', because a corrosion inhibitor can't be used. I have a Vailant combi with microbore (10mm) feed to the radiators. Can I use this TR or have I got to get another type?

[MORELLO]

Interesting. I don't know but will be watching as I was going to do the same...

[buildersmate]

The instruction appears confusing to me also. With a direct HOT WATER system, the water in the hot water cylinder has previously been through the boiler to get hot. This contrasts with an indirect hot water system, where a heat exchanger coil in the cylinder supplies the energy to heat up the water in the cylinder, and the water in the boiler just goes round and round, never getting out. The same water is invariably used to heat the radiators. I am sure you know this, and such water normally has inhibitor in it to prevent the inside of the rads (mild steel) corroding with black magnetite. I think your TR is mild steel, and if so it would be perfectly suitable to substitute for the existing rad, with inhibitor. What I think the instruction is trying to warn you against is fitting the TR in a direct hot water system. In such an arrangement, the TR forms part of the hot water system and the water flowing through the TR eventually emerges from a hot tap. In this arrangement, the TR must be made from stainless steel to stop the inside corroding. (The advantage of such a set-up is that you can run the TR in the summer without running the rest of the CH). But I accept that's not what the note appears to say.

[Hard@it]

I don't see any problem if you are using a sealed system which your combi is, just go ahead and fit it.