Taking a feed from an FCU for a thermostat

My combi boiler is connected to an FCU that joins the ring main. All well and good and proper. Now I have a HC60 relay unit that needs connecting to the boiler. It is the receiver for the CM67 RF programmable thermostat.
My question is, can I take a connection from the FCU to the HC60, so that both the boiler and the relay work from the same FCU. It means that if the switch is off, neither the boiler nor the relay/thermostat will operate but that's OK because we wont need one without the other will we.
Schematically this will look like...
Mains-----------[FCU]--------------Boiler | |----------------HC60 Relay/CM67 Thermostat
Otherwise I'll have to break into the ring and add in an extra FCU for the relay, which seems to be a bit over the top to me.
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In an earlier contribution to this discussion,

What you're proposing is fine - except that your diagram makes it look as if you plan to connect to the supply side of the FCU, whereas you must, of course, connect to the outlet side. That way, the whole heating system can be isolated by turning off a single switch - which is the way to do it.
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wrote:

No, you definitely want everything related to the CH to go through one switch and fuse or one day someone will have a nasty accident.
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