Pressure operated valves

I have thermostatic radiator valves on both the upstairs and downstairs heating circuits, and one radiator on each circuit which has lockshield valves. The radiator on the downstairs circuit is at the end of the run, which means there is always a bit of heat in the pipes to keep the cellar aired (I have the return pipes unlagged).
I am fed up of fiddling with the bypass valve which is only a 15mm gate valve (the boiler manual says it should be 22mm) and seems to get blocked with crud every so often, and I bought a pressure operated valve which I was going to put in the by-pass circuit. However I fell to thinking, what say I put the pressure relief valve in parallel with the motorised valve for the downstairs circuit? Then when the heat demand was fulfilled instead of raising the airing cupboard and the corner of the spare room to an unreasonable temperature water would circulate around the downstairs pipes and help keep the cellar aired. Also the longer run would cool down faster than the bypass loop (which I suspect is shorter than the minimum 6ft specified in the manual).
Any thoughts?
J.
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John Rouse

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On Thu, 05 Feb 2004 19:30:18 +0000, John Rouse wrote:

To summarize just so I have really understood: You want to put the bypass valve in parallel with the heating zone valve. The water will be forced through this valve during pump over-run time and circulate through the far radiator via the cellar.
I think this would work provided you got the right setting for the bypass valve and you made sure that the far radiator could not be turned off (2 locksheild valves?)
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Yup, that's it in a nutshell.

Yes, that's what it's got at the moment.
J.
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John Rouse

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I assume two zone, 1 up, 1 down. I assume each with a time clock and stat. So downstairs is off by the clock and TRVs open, and upstairs is on. Upstairs is then satisfied and the stat closes the zone valve. The boiler is in over-run and then the auto bypass opens and sends heat to the downstairs rads which don't want heat. Best have the airing cupboard overheated.
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