I assume you have spring-return valves, rather than motor open/motor close (MOMO) valves. I share your frustration with the recent consolidation of heating control design such that all valves always close when there is no boiler demand, necessitating the boiler bypass and wasting energy. Even the HR92s (which are MOMO hardware) are controlled as if they are spring-return, and so close fully if there is no boiler demand. That creates a noisy opening stroke in the mornings, unnecessary valve wear and battery consumption. It would be preferable if Honeywell's control logic told the HR92s: "stay where you are", when there is no boiler demand. That way there would be only small (and quieter) adjustments when the heating cuts in again in the morning and there would be a useful destination for the boiler and pump overrun.
But for your specific question about a "box of tricks" to keep a zone valve open, as Paul Lockenden has noted above, DB Mandrake posted a very smart wiring scheme that uses the pump demand to hold at least one valve open, which works for spring-return valves. He posted the schematic at:
That will only work if you have only two valves (one for CH, one for DHW). If you have more valves, then you will need to create a smarter "box of tricks". I use MOMO zone valves, and I use a multi-pole boiler relay to isolate the 'close' signals to the valves, so that they will only close if there is boiler demand. That means that I will always have at least one valve open (as the boiler demand comes from the open limit switch on the valves). I wrote a rather self-indulgent lengthy piece on the shortcomings of current valves that are available for domestic use, which is at:
But for your specific question about a "box of tricks" to keep a zone valve open, as Paul Lockenden has noted above, DB Mandrake posted a very smart wiring scheme that uses the pump demand to hold at least one valve open, which works for spring-return valves. He posted the schematic at:
That will only work if you have only two valves (one for CH, one for DHW). If you have more valves, then you will need to create a smarter "box of tricks". I use MOMO zone valves, and I use a multi-pole boiler relay to isolate the 'close' signals to the valves, so that they will only close if there is boiler demand. That means that I will always have at least one valve open (as the boiler demand comes from the open limit switch on the valves). I wrote a rather self-indulgent lengthy piece on the shortcomings of current valves that are available for domestic use, which is at:
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