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Independent control it what it says is required for a new build house over a set area, I would think with TRV's fitted to every radiator that is independent control, and using electronic heads one can even include time, not expensive at £10 each head.

However the condensing boiler has a problem using return water as it's control, it can never turn completely off, it modulated down to minimum output then it starts to cycle, and unless a wall thermostat or you get some manual intervention it would continue to cycle all summer.

Although a off/on thermostat works to an extent, it can also result in the boiler not modulating correctly which costs money, so many boilers today have assess to the ebus and use modulating thermostats OpenTherm is a good example, although there are some manufacturers which use their own version.

So to comply with the legal requirement for independent control one would need two modulating thermostats one for each zone, however I can find out how you connect two modulating thermostats to the same boiler? There must be a way, a hub or something, but can't find it.
 
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Independent control it what it says is required for a new build house over a set area, I would think with TRV's fitted to every radiator that is independent control, and using electronic heads one can even include time, not expensive at £10 each head.

However the condensing boiler has a problem using return water as it's control, it can never turn completely off, it modulated down to minimum output then it starts to cycle, and unless a wall thermostat or you get some manual intervention it would continue to cycle all summer.

Although a off/on thermostat works to an extent, it can also result in the boiler not modulating correctly which costs money, so many boilers today have assess to the ebus and use modulating thermostats OpenTherm is a good example, although there are some manufacturers which use their own version.

So to comply with the legal requirement for independent control one would need two modulating thermostats one for each zone, however I can find out how you connect two modulating thermostats to the same boiler? There must be a way, a hub or something, but can't find it.
Eric The water heaters has 2 heating elements 1 on top and 1 bottom and they both have thermostats witch can control both elements separately
 
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Eric The water heaters has 2 heating elements 1 on top and 1 bottom and they both have thermostats witch can control both elements separately
The water heater may have two stages, the pre-heater gains the latent heat, and the main part heats it further, and to ensure the pre-heater works the return water must be cool enough, so the modern boiler is designed to modulate, well boiler is a poor name, as if it boils there is something wrong.

So typical output is 8 to 28 kW, and in the early years the boiler was controlled by the return water temperature, but today assess to the ebus may be available. This is in the main gas boilers, the oil boilers don't lend themselves to being modulated.

Electric can't really be modulated, not sure if really needed, but using a mark/space ratio or wave form chopping the input can be varied, can see the point if trying to match electric use to solar panel output, but in the main simple off/on with 20 minutes or more between each heat cycle.

The problem is therefore really limited to gas boilers, we want them to modulate, but using zone valves controlled by a off/on thermostat is likely to stop the boiler modulating correctly.

So using a modulating thermostat connected to the boilers ebus seem to be the way forward, but then the two zones are not independent.

It now seems the independent bit is what the approved document asks for, but the law does not ask for this, some one who wrote the interpretation (Approved document) it seems got it all wrong?

So having a single thermostat to turn off the boiler to stop is cycling is OK, using programmable TRV heads without any motorised valves it seems is OK.

Unless you know some thing different?
 
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