I'm sorry I will come clean: I don't know everything and have to occasionally lean on other sources for information. Some of our computers even have Google installed.

Last week, two heating engineers called with reference our new monobloc system. Monoblocs are mounted outside so, in the event of power failure, it's possible that they will freeze up, causing serious damage. To prevent this happening, glycol or anti-freeze is added to the water. The problem with anti-freeze is that is circulates around the whole circuit so it can be a large volume and it's quite expensive at about £1 a litre.

Last week, I got two phone calls on the subject of PTFE and its use on systems with glycol in them. There appears to be a rumour circulating that PTFE fails if used in a system containing glycol.

I don't know who started this one, but I had to go and ask an expert. My dad is a retired professor of chemistry, his speciality being polymers. I called him and asked what he made of this theory. "Utter rubbish", he said. "PTFE is completely inert. That's why they use it. Glycol will have no effect on it whatsoever. The biggest thing about PTFE is that is doesn't react with anything."

So there you have it; keep using PTFE - it will be fine, glycol or not.

You heard it here first. Thanks dad.