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I seen on this forum many times where people use on/off wall thermostats to control the home temperature, and in my mothers old house we had a Honeywell Y6630D thermostat that had built in anti hysteresis software which started to cycle the boiler off/on as it approached the target temperature which to be fair worked very well, however not so sure if it saved any money by not over shooting, as each time boiler switched on it was at max output, so in theory a very simply wall thermostat and using the TRV's to control room temperature would be better, the wall thermostat wants a high slewing range around 1°C so once it does switch off it stays off for a reasonable time.
However using TRV control with wall thermostat and setting up so wall thermostat only turns off when whole home is warm is hard enough, but add some zone valves and in essence you have zone valves controlling zone valves as each TRV is a zone valve really and it becomes really complex to get a boiler to run with a OpenTherm thermostat with double zone valves and no area where it is always heated to actually put the Opentherm thermostat.
So we end up with an unworkable system, looked at EvoHome, Wiser, Tado etc, non seem to interconnect with old zone valves, they will all interconnect with TRV heads, but the old zone valve is still found even in new homes.
So this is the question, if some one ripped out the silly zone valves and fitted all programmable TRV heads instead connected to an OpenTherm thermostat so the boiler modulated as it should, what difference would it make to the heating bill?
In other words although we all know zone valves are stupid and only work with oil non modulating boilers is it ever worth the cost to correct, we can make zone valves work but not in theory efficiently, so nothing to do with comfort and having each room at correct temperature, that is not the question, the question is having a boiler modulate and gain the latent heat how much money will it really save?
However using TRV control with wall thermostat and setting up so wall thermostat only turns off when whole home is warm is hard enough, but add some zone valves and in essence you have zone valves controlling zone valves as each TRV is a zone valve really and it becomes really complex to get a boiler to run with a OpenTherm thermostat with double zone valves and no area where it is always heated to actually put the Opentherm thermostat.
So we end up with an unworkable system, looked at EvoHome, Wiser, Tado etc, non seem to interconnect with old zone valves, they will all interconnect with TRV heads, but the old zone valve is still found even in new homes.
So this is the question, if some one ripped out the silly zone valves and fitted all programmable TRV heads instead connected to an OpenTherm thermostat so the boiler modulated as it should, what difference would it make to the heating bill?
In other words although we all know zone valves are stupid and only work with oil non modulating boilers is it ever worth the cost to correct, we can make zone valves work but not in theory efficiently, so nothing to do with comfort and having each room at correct temperature, that is not the question, the question is having a boiler modulate and gain the latent heat how much money will it really save?