Regarding the elect. supply to a new gas central heating system...
Is it ok to run a T&E from a dedicated mcb in the CU to supply both
the boiler and the pump?
What should the termination be on the wall? Does it need some kind of
isolator (as in eg an electric cooker DPole switch) .
I have done exactly this.
I used a 6A MCB in the consumer unit. Ran 1.5mm2 T&E from this to a
double pole Fused neon connection unit in a pattress box.
Then onwards to the wiring centre that your pump, boiler, thermostats
and valves connect to.
PLace a label on the switched FCU to indicate its a an isolator for the
You should also place a FCU on the supply cable to the boiler and place
this adjacent to the boiler and label this "BOILER ONLY" Isolator.
This was on the advice of the gas engineer so that they can quickly turn
off the power should the need arise. In my case, there is 240 mains on
the zone valves so hence the labelling as flicking the boile ronly
isolator won't cut the power to the zone valves.
Obviously if your system isolator switch is next to the boiler, then the
situation described won't arise, but I suppose an issue would arise for
anyone working on the pump or zone valves if these are in a seperate
room to the boiler.
Most boilers would require triple pole isolation and not a FCU for local
isolation (they usually have permanent live, switched live and the neutral).
Even if you did not need the triple pole isolation and could get away with
double pole isolation a non fused double pole switch next to the boiler
would be recommended.
And the OP MUST have a switched fused spur somewhere that will control ALL
of the boiler controls and the pump.
Normally a flex outlet for the boiler (perhaps with neon), and then a
main double pole switch somewhere that will isolate both the boiler, the
pump, and any other mains control equipment such as 3 port valves etc.
There is a lot of benefit in running your heating system on your own MCB
and even on a RCBO instead. You then have integrity of supply so that a
falut elsewhere in the house does not lead to loss of heating during a
My CU has 13 RCBOs. as the boiler and dassociated controls are on their
own RCBO, I can have all of the other 12 RCBO's trip due to overload,
earth leakage what have you, but still have power to my boiler. I have
automatic frost protectino on the boiler so hopefulyl will prevent burst
I think a dedicated RCBO for the heating only is a a small price worth
paying for that extra level of assurance during deepest winter...
Particularly when you see how much devastation leaking water can cause.
My particular boiler has earth, permanent live, permanent neutral and a
a pair of volt free connections. These volt free pair goes to all the
microswitches in the zone valves so I don't have a switched live per se
as ARW points out.
Fair enough, but one significant risk during cold snaps is a power cut.
In order to cater for this, everything in my system is powered from a
single 13A plug - which can be unplugged from the ring main and plugged
into a generator instead. [And yes, the genny does have an earth spike
and has one side of its output tied to earth to keep my boiler's flame
ionisation detector happy].
It also means that I can achieve total isolation of the system by
pulling the plug.
For clarity, I was not suggesting otherwise. On its own circuit is a
very good idea. Note that single module RCBOs, and normal MCBs don't by
themselves provide isolation though - so you still need a double pole
I have a wiring centre fed by a FCU with neon.
two 2-port zone valves, two programmable room thermostats connect to
this along with a five core cable for the boiler. (one of each for each
floor of house.)
The programmable thermostats control the zone valves directly, the two
microswitches within the zone valves are wired in parallel straight to
the volt free contacts to the boiler.
The boiler needs permanent live and permanent neutral as its a combi
boiler otherwise we get no hot water :-)
I already have this (the Neon FCU) in the airing cupboard which also has
the 2 zone valves and the wiring centre.
Then there is 5 core cable going from airing cupboard to the boiler in
Hence the need for a isolator switch next to the boiler for anyone
working on the boiler to be able to turn off power quickly without
needing to run to the airing cupboard.
probably could actually, replace the tank stat with a 2nd room stat, and
and relabel the HW on the timer to be the 2nd heating zone.
The boiler can be reconfigured to work with switched live instead of
volt free switching contacts.
To be honest, having two programmable room thermostats, two 2-port zone
valves etc is actually simpler to wire, understand and fault find than a
But bear in mind that the cylinder stat on Y-Plan is a change-over
switch - not just on/off - so your second room stat would also need
changeover contacts. [In reality, most do, so that they can be used for
both heating and cooling applications].
That is a very good question.
if its a boiler that just has earth, neutral, live and switched live
then a 3 pole switch like those used on bathroom fans with a neon and a
fuse (if they exist) would be do.
My boiler is five wires, earth, permanent neutral, permanent live,
orange and grey wires.
The grey and orange wires just go to all the paralleled up microswitches
in the zone valve.
So in theory a simple 2 pole fused neon switch would suffice. However,
as there is permanent live and permanent neutral to the control wiring
centre, in theory, if a thermostat starts calling for heat, a zone valve
will be energised and open.
So there is a theoretical risk that live mains could contact upon the
zone valve microswitches, and hence make ornage and/or grey live in the
At least the two zone valves have un-pluggable cables so power can be
cut to the zone valves in an emergency.
SO I suppose I could move the isolator switch from airing cupboard to
the kitchen where the boiler is and power the wiring centre from the
Why would you not just feed the live from the two pole isolator that
turns all power off to the CH through the end switches?
After all it would remove all power including that from the stats and
the end switches (one hopes).
What is more problematic is feeding the 24v loop through the zero volt
end switches when the five core flex also has 240v ac on it.
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