2 Wire Wireless Installation

19 Mar 2003
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United Kingdom
Combi boiler is Main Combi 24 HE.
Optional integral timer fitted, but new baby means it's running 24/7 being controlled by Siemens RAA20 thermostat in the hallway (2 wire 230V control).
Thermostat run on 3C&E (third core & earth unused).

Not ideal heating the house based on the hallway temperature, so bought the HRFS1 wireless thermostat.

It looks like there isn't an easy way to replace the wired thermostat, without chasing wires etc.

Wireless Thermostat Manual
Wiring for 230V app
SL (Off)
SL (On)

Wiring for External Thermostat Loop
COM - Live Feed from boiler external thermostat loop (volt free feed)
Norm Open - Switched live back to boiler (volt free switch live)
L - Live Mains
N - Neutral Mains

The boiler manual says thermostat loop is 230V switching.

I can't fathom how to wire using the diagram for 230V application.

The diagram 'for external boiler thermostat loop' seems straightforward but mentions volt free feed/switch.

My thoughts were to disconnect hallway thermostat, and wire wireless receiver in next to the boiler using a spur from the boiler feed as a mains supply, but would the 230V switching from the boiler be OK to wire into the wireless receiver (even though it mentions volt free)?

Apologies for the length.
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Yes that would be fine.
What i do and most others (Im Assuming) do is obviously at install stage but we/I come off the actua live feed to the boiler internally as your receiver will still need to be wired to the boiler to receive info from the stat.

Put Live and nuetral in there correct live and nuetrals (spur to boiler wires) and then your com and and back to where the wires from the stat are on your boiler (1 and 2 normally) and then earh to earth.
i fit remeha boilers and this volt free business is confusing if not using own brand stats and programmers.

usually for volt free you need to remove a link from the transmitter between Live and NO (normally open) you then wire the transmitter as advised in Manufacturers instructions.

you then need to bring a live and neutral to transmitter, i use ports from within the remeha pcb (x2)but if it is easier for you to do it from the fuse spare thats an option.

im not aware of the stat you are using so might be totally differant set up.
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thanks a lot for the quick reply.

Will give it a go. Was just a bit worried about wiring 230V where it shouldn't be going and frying the boiler PCB or the thermostat.

Once again many thanks.

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