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Don't be silly, it's clearly the chimney cleaner button. Pressing it injects gas into the out pipe. This is followed by a microprocessor controlled spark initiation sequence which initiates a hyper conductive event and by DNA replication (as seen on CSI) instantly cleanses the exhaust orifice of all waste matter (except where such an event is prohibited by local ordinance and social acceptability).

As you undoubtedly live in a non-approved area the inbuilt position sensing module has disabled the feature to ensure your continued well being.

Blast air out to clean the flue???

Looks like a sweep and his ladder to me...

It's actually officially referred to as the "chimney sweep button" in the manuals on the Bosch Greenstar range. Not really a user control as such but used in combination with others to enter the service mode.

This is the euroglyphic for testmode. I'm surprised you've not seen it before, do they have no Vaillant suppliers on your patch?

You'll find this on a number of models. I'm fairly sure that you hold it in for a number of seconds and then the boiler goes flat out for a period of time or until something is about to overheat.

Nice to see the EU following its long established tradition of clarity and understandability when it comes to such things.

Test mode = anorexic man carrying ladder while wearing top hat - obvious innit?

Which manuals are you looking at? The User and Inst&Service ones for this actual boiler say it's 'Central Heating Boost Button'

Sounds like you're talking about the spanner one - the other W-Bs I've put in recently (i-junior & variants) all have this and as you say if you hold it in for 10s or so it goes into full-bore mode. I'm not sure I'd put an engineer-mode button on the front panel, least of all amongst user controls, but I fear W-B have rather lost the plot (or their engineers have lost out to pointy-haired managers & 'designers') when it comes to user interface design.

F'rinstance:

1. take the 'Eco' button, which switches OFF the DHW pre-heat. It'd be more logical (IMHO) to have a button to switch this ON, but 'eco' obviously has more cachet (to a certain mindset) so you now have a switch which you switch ON to turn OFF a function. If they really wanted to be 'eco' (and were prepared to spend a minute amount of money on it rather than just choose a trendy label) they could have made the pre-heat controllable by a timer.

1. Worse, they even have this (now redundant) control on the non-combi version (12i or 24i System).

2. all the LEDs are so pastel-hued you can't actually see them unless it's pretty dim in the room.

That'll be it then! I'll dig out my asbestos underpants for the commissioning :-)

Hold in for 10 seconds, flat out for 15 minutes..

Indeed, not to mention the waste of energy (however small, it's the principle) for that little green lamp

If they really wanted to be

Tis on my 24jnr. the Hot Water part of the dual channel timer controls eco mode. Not that I've found the pre-heat any use. At best you get, cold from the dead leg of pipework, then a slug of hot that was sitting in the boiler, then another shot of cold while it starts up. Unless used very recently, in which case the pre heat isn't needed

? I find the blue (very 'in' these days it would seem) on-light (reminds me of the flame window of an old Ascot) a pretty effective night light.

Yes, mine (MAN Micromat) has this as well.

It's used when adjusting the settings on the gas valve during commissioning - it can be pressed and then the fan speed wound up to the top and down to the bottom while CO2 levels are measured.

Sorry, John, my post was only in reference to the Bosch Greenstars that I am more familiar with, I assumed that the button would be generic across the entire range. I just had a quick look again and on the W-B models with the Bosch Heatronic controller such as the Greenstars the button doesn't provide any boost.

The message from Peter Parry contains these words:

Me, I'd have had the spanner as testmode.

To be used by femaoles only. It gives the heating a boost to raise the temperature so you can lie naked on the bed and wait for Robin Askwith[1] to come along.

MBQ

The message from " snipped-for-privacy@hotmail.com" contains these words:

Just pray it doesn't turn out to be George Formby.

P'raps there's a market for add-on blue neon lights illuminating the underside of the boiler? :-)

Not sure I'm with you there. This _is_ a Greenstar (i.e. current condensing model).

You mean you're not giving fluffy dice with every installation like BG do ? ;-)