I have just finished fitting a new combi central heating system and no
need too add a room stat to the system. I have looked around and foun numerous models ranging from £10 upwards. Do I need too run an independant 240v supply to the stat or doe th power supply come from the boiler unit itself? Any advice greatly appreciated
-- brian
If it's purely a stat, then it's only a switch operated by the heat in the room, so it doesn't need a "power source". The power which it switches is in the boiler.
Thanks for that, thats the answre I was hoping for. Didn't want the hassle and mess of having to chase in for new electri supply
-- brian
well you still have to run it back to the control unit - and its usualy a 4 wire (three plus eatrh) cable. Live in. live out and neutral plus an earth...
It doesn't normally control the boiler directly either.
Its more usual that the timer feeds the live to the stat, when timer calls for heat, and the stat live return feeds the motorised valve that open the CH water circuit to the boiler, and the motorised valve switch then controls the boiler.
For energy saving and greater comfort fit a programmable type. These are battery operated - the battery lasts a couple of years - so only need the switch pair to them.
I am refurbing a house to sell on and so want to keep costs down, henc opting for a inexpensive basic stat.
In reply to natural philosopher, I realise that I need to run a cabl back to the control unit from the stat. But according to th installation manual there are only two connections to be made at th boiler.Therefore I don't understand the reference to the 4 wire cable. Am I missing something
-- brian
'Mains' stats have a mains operated accelerator coil which needs both a live and neutral to work their best. The common way to wire them is with
1mm triple and earth cable.But you could omit the shunt coil if switching a low voltage control line as many modern boilers have, as the thermostat will still work as a plain switch, but not so well. However, I'm not sure this conforms to the regs these days - I suspect not.
Just to complicate things, there are radio room stats available. The 'reciever' is attached to the boiler, and you can play about with the position of the 'sender' since there are no wires involved. Bit more pricey though.
AFAIK the regs (Part L in this case) only require a thermostat. It does not specify how well it has to work, although it may be implied/assumed that it should be installed according to the manufacturers requirements which for non-electronic ones would mean using an accelerator heater and supplying mains and neutral.
If the OP wants 'volt free' then an electronic type would be better.
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