"The Natural Philosopher" wrote in message
...
Dave Baker wrote:
The electrickery bits of central heating are absolutely not my thing but
I can't see why, with any boiler, you can't have an external controller
driving the zone valves and stats which produces a single output to the
boiler telling it when to switch on.

You can.

If the boiler has a way of accepting such input.

This one does not.

Its completely integrated and comoputerised, and the only thing apart from
the mains that it takes, is a 'smart' room stat made by the manufacturer
ONLY.

If the "room stat" is actually a temperature sensor using a resistance to
detect the temp (the usual method), opening the circuit will usually send
the thing one way or another. I have done this many times in designs on
commercial setups. The boiler fully on or fully off. So inserting a relay
in the line will switch on or off the boiler. Then this circuit can go
though the end switches of the zone valves. When the zone valves are open
the whole circuit is engaged and the temperature control is working well.
When closed the boiler is off or on. I would guess than when this temp
sensor is linked out (no resistance) the boiler will be full on.

It is worth full linking the stat circuit and opening and observe what the
boiler does. Then close and see what happens. I would be leaning to that
the circuit is just a low voltage resistance temperature setup and what I
describe will easily work.

If so, depending on the zone valve a relay have to be incorporated in the
design. Best have a SPDT end switch on the zone valve, if possible.

Its highly UN-obvious. Thats someone has finally produced the plumbers
dream and the DIY-ers nightmare. A boiler that doesn't need any electrical
installation, beyond hooking up to a switched fused spur and turning it
'on'..

That is the aim of many makers - fit and forget, no need to design as the
experts do it for you. Also getting around Part P using a wireless stat.