It has been suggested to me that the new boiler I am having fitted, a Worcester Bosch Greenstar 28 HE, may not be compatible with the existing room stat, Honeywell type CM67 RF with Optimum Start.
Whilst I wait for a reply from the manufacturer, has anybody any experience of this combination?
Chris
There as far as I know only three ways a boiler in externally controlled.
1)By feeding it 230v AC on to a dedicated terminal. 2)By connecting together a pair of terminals. 3)By running it in series with the circulation pump.3) Is very rare and no modern domestic boilers work that way TTBOMK.
(2) Is becoming the norm in place of (1).
The boiler in question will be one of the (1) or (2).
And presumably, therefore, can happily be controlled by a CM67 RF - since this has a volt-free change-over contact which could be connected directly to the boiler for (2) or could switch a mains feed for (1)?
Not specifically, but I'm sure it will work. I have the boiler and wired it up to a control system and can't conceive of how a general purpose thermostat could be made that wouldn't be compatible with it. Bosch make some specific room stats that have extra features only possible with something more sophisticated than an on/off signal, but this isn't compulsory. I don't use their system as I have an S-Plan+ and the Bosch specific system doesn't subzone well.
Christian.
IIRC, it accepts a 230V signal to fire, which is the easiest to supply. You connect volt free contacts between the boiler permanent live out and the call for heat input. You must get the live feed from the boiler permanent live output, as the boiler has an internal isolator which must be effective. In fact, all electrical supply to the central heating system (except the immersion) should go through the boiler's internal isolator.
Christian.
Not so. You can have a main switch to the CH and a local isolator at the boiler, as long as no external feed enters the boiler when the isolator is off. This is how two boiler setups are done. One main and local at the boilers.
Obviously, you may have additional external isolators (I have two on my system), but the internal isolator must be used. Any control electronics must use the internal isolator output such that the live potential may never appear on the signal terminals when the isolator is off. Worcester-Bosch are very clear on this in the installation manual. This could make multiple boiler setups quite difficult in some cases, perhaps requiring an additional relay.
Christian.
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