(I can't find any evidence that this post made it to the newsgroup - apologies if it's a duplication ...)
Sorry if it's a dim question - I've done some Googling but can't find an answer ...
Discussing draining, flushing and 'servicing' the heating system "when the Summer comes" (!) with a friend today, I said I intended to replace all the radiator valves (old system, hard water, valves not operated for years, most of them stuck) and to use TRVs. Friend said when using TRVs there must be one radiator in the system NOT fitted with one, but he was unable to explain or justify this assertion other than by claiming "British Gas says so" (he has a maintenance contract with BG for his system).
Is he right? Shirley it can't be to ensure there's still a flow when everything's up to temperature because the 'non-TRV' rad could still be turned off manually ... and if this were to happen, there will still be flow through the boiler by convection in a 'gravity' hot water system anyway ...
"Confused" of Hatfield.