Not sure I fully agree with Wiring Matters > Years > 2025 > 107 - September 2025

mapj1 said:

Its main use is not for us to work on it once in a blue moon, but for the householder to turn the water heating off when not needed - while on hols or similar . 

Or to turn it on once in a blue moon when the boiler has conked out.

Sergio Fernandez said:

Personally I think Rotary Isolator would be far better than 20 amp Double-pole switch

These devices would also likely be suitable if rated AC21A (i.e. suitable for switching resistive load on-load) and certainly in non-domestic premises might be preferable.

Alan B said:

Personally I have found a fair number if burnt out fused switched spurs in immersion circuits, I generally also install 20A double pole switch with Neon. The diagram showing markings on a switch approved for isolation is interesting. I can only see one switch from hager that has this sort of markings. Not having access to BS EN 60669-2-4:2005 I wonder if the markings are actually a requirement?

I can answer this ...

Not all switches to BS EN 60669 series are isolating switches ... as we can see from Table 537.4 of BS 7671, from BS EN 60669 series, only those to BS EN 60669-2-4 are listed as suitable for isolation:

In terms of marking for isolating switches to BS EN 60669-2-4, the marking for isolation should be visible once the product is installed:

'OFF' and 'ON' are suitable alternatives for Ι and Ο.

If the switch conforms to another part of BS EN 60669 in addition to BS EN 60669-2-4, it will be suitable for isolation, BUT it should be marked as above.

Not like you to post such gibberish Mike presuming this post was meant as a reply to what I wrote.

Gary

Personally I have found a fair number if burnt out fused switched spurs in immersion circuits, I generally also install 20A double pole switch with Neon. The diagram showing markings on a switch approved for isolation is interesting. I can only see one switch from hager that has this sort of markings. Not having access to BS EN 60669-2-4:2005 I wonder if the markings are actually a requirement? Although as others have said if you actually want to isolate an immersion heater it would probably be done at the the consumer unit.

On the suggestion of a rotary isolator I think it just looks out of place inside a home and I would only use one if essential for safety requirements.

if you can lock it off at the CU and are feeling cheap you can probably drop the switch rated for isolation part altogether.

Its main use is not for us to work on it once in a blue moon, but for the householder to turn the water heating off when not needed - while on hols or similar . 

Fused spurs only make sense when the supply (dedicated or shared with others), is of a higher rating - e.g a 32A ring. 
To me another obvious fix if you must have one, may be  to put the fused spur unit outside the cupboard. much as one used to put conventional light switches outside bathrooms. being visible  also reduces the risk of it being left in the wrong state for a long time.
Mike

I. have come across many heat damaged spurs and the occasional socket over the years supplying immersion heaters so agree with that part. I personally always fit. a 20 amp DP switch. I don't see the need to have to lock it off as you will be working right next to it. If it needs locking off for other reasons do it at the consumer unit as it should be a dedicated circuit although I have seen an odd boiler or heating control tagged onto the same circuit.  Rotary switches are clunky and could be prone to being inadvertently damaged or knocked off the wall in an airing cupboard.

Gary