Is this switch really suitable for an 18kw boiler?

[Fluffycloudland77]

It looks more like a fan switch, doesn't it?.

It's not dirty, I wasn't too careful when I painted because I knew we'd change the sockets etc.

It's a gas boiler right? If so The 18kw is the output power from the gas. The electric will just be powering the pump and valves about 0.1kw.
For boilers with external controls there is a neutral, switched live to tell the boiler when to come on, and a permanent live so the boiler can do the frost protection and other protection actions.
This means you need a switch that can switch 3 wires at the same time. By coincidence that's exactly what a bathroom fan needs.
So what you have is fine, but it's good to be sure!

Oh lord why didn't I think of that? no wonder people talk about just plugging boilers into a wall socket.

www.electricalcounter.co.uk/products/Switches+%26+Sockets/Nexus+Metal/Nexus+Metal+Brushed+Steel/Metal+Brushed+Stainless+Steel+20A+Double+Pole+Switch+with+Neon/2551520349

Would it be wrong to replace it with this? There's a fan one in the range too but this one would look neater on the wall.

It would indeed be wrong, triple pole is the key word you are looking for. That one is double pole.

Although technically the only "all pole" isolation you need in a single phase installation is the main switch, usually the manufacturer's instructions specify an "all pole" isolator near the appliance for servicing reasons.

It may not be three pole, it depends where the switch is wired.

The supply from the consumer unit to the boiler controller will only be two wires, line and neutral, and should have a double-pole switch for total isolation when needed. It will normally be fused at 3 amps.

If you take out the two fixing screws you can soon see how many switch poles it has wired.

Thank you both. The one I linked to was suggested to me by the supplier I'm buying the switches off.

I'll buy the fan one instead & hopefully not look an idiot when Dh comes to fit it.

It's a good idea to have a switch with a neon indicator to show when the boiler supply is on. Just gives a bit of confidence. But do check the existing switch first.

The switch you have got is almost certainly incorrect. It is not fused and is designed for low currents.

It is normal for boilers to be run off the socket circuit. This is "fused" at 32Amps, because it is expected to be able to supply several appliances such as dishwasher, kettle and toaster.

The boiler should be fused at 5A or thereabouts.

In the UK this is easily achieved using our wonderful BS1362 system.

You need a switched, fused connection unit (FCU) such as this one by Crabtree which is a good maker.

The switch enables it to be safely isolated for servicing, the neon indicates that it is turned on, the fuseholder enables you to fit a 5A fuse like this. (they are usually sold in packets of half a dozen or so, get enough to fit in the plugs of table lamps, radios etc). Brown fuses are 13Amp which is too much.

That's a very good point that they may have only needed 2 poles but if they only had a 3 pole they used that instead. Good one to check.
And the fuse is optional e.g. our boiler has a dedicated circuit with a 6a circuit breaker, so it's fine to use a switch for isolation. However if you connect it to the 32a ring you'd need a fuse.

"This means you need a switch that can switch 3 wires at the same time"

No you don't.

Can I use this if I put a 5amp fuse in?

www.electricalcounter.co.uk/products/Switches+%26+Sockets/Nexus+Metal/Nexus+Metal+Brushed+Steel/Metal+Brushed+Stainless+Steel+Fused+Connection+Spur+Unit+13A+Switched/3116500630

Not really fussed about neon.

Yes, that would do fine. But you must replace the fuse with a 3amp one.

Just check that the existing switch has a box behind it that is at least 25mm deep. Some are shallower than that.

Just to clarify, a 5amp fuse would be OK but it's a higher rating than you need. As a basic principle you should limit fault currents as much as possible. If it's taking even 3amps, something is seriously wrong.

PigletJohn your 3 word explanation after misquoting without my precondition is not very useful. Given the lack of information, you have just made different assumptions then me. In a boiler with external controls, which core would you not need to isolate out of the 3? Or would you isolate the controls through the same switch? If the op has a setup as I specified, they will need that switch.As per my later post, it's possible all are not used, but I'm trying to help the poster.
Oh and that switch isolator is certainly designed to handle currents taken by a boiler, it's not likely to fail to break any current within the rating of the protective device.

And Gladallover, you have to make sure the fault current is high enough to blow the fuse in time, that would be 0.4 seconds for a portable appliance and longer for a fixed boiler. As long as the cables won't exceed their rated temperature then the protective device rating is fine. Although the manufacturer's instructions override all that and most specify what you need.

What I have in mind, for an isolating switch for the boiler and heating system, is that it will be used to make it safe for maintenance.

The maintenance may include opening covers, replacing controls or working on wiring.

So the isolator must be upstream of all timers, programmers and thermostats.

So it must not leave any control which might require a permanent live, and provide a switched live, unisolated.

Therefore, there is no need to isolate a switched live, because there is no control connected to the supply which can give one.

If you have a 3-pole switch it implies that there must be a 2-pole switch elsewhere to isolate the controls. In which the 2-pole switch is the isolator and the 3-pole is redundant.

The MCB for the circuit is not considered a suitable isolator since (in the UK almost invariably) it will be single pole.

If the isolator used does not incorporate a fuse or other overcurrent device, it must be rated for the circuit to which is it connected. In the UK this will most often be a 32A ring or a 20A radial, so a fan isolator would usually be unsuitable.

There's a normal rocker switch in the hot water cupboard. If you switch it off the heating control panel for the water goes off & the boiler goes off completely.

(the 20A switch on a 32A RFC may seem strange, but remember it is feeding an FCU which is used at 13A or less - see email from Mark Coles at the IET

PigletJohn thanks for the update,I think we're basically agreeing just about different things :)
And now the op has given the extra details, we know that their setup is safe from that point of view. Although a lockable fcu would be enough in some people's eyes for safe isolation, other people servicing a boiler want to see a switch in the same room as the boiler. I've seen many reports of British gas asking for them, and if I were servicing a boiler I'd prefer one.
Seems from my renting days most servicing just involves opening the boiler and cleaning, adjusting and testing various things. And going out to look at the flue terminal. One house the pumps and control centre were hidden in the ceiling and the programmer was tiled into the wall but that boiler had a notice saying isolate in two places.
So in response to the op, in your setup you could even put a blanking plate and wire straight through, but you might get complaints from the person who services the boiler!

There's a normal rocker switch in the hot water cupboard. If you switch it off the heating control panel for the water goes off & the boiler goes off completely.
Thant's interesting. On the face of it, that switch is doing the same job as the one you are replacing, and there is no need for two unfused switches in series.
In this case it would be inappropriate for anyone here to speculate on why there are two switches like this. I think you should get an expert opinion on how the supply to the boiler is actually wired.

I'll ask the chap who services the boiler. Hopefully he'll know.

Yes. Get him to explain what the two switches do.
I most certainly wouldn't wire out one of the switches as suggested above, unless the boiler man says it's redundant.

Sorry yes I actually misread, replying on my phone! Yes if it's a normal switch it might not be double pole, and it's supposed to be clear whether it's on or off which it wouldn't be.