21 Nov 2021
Reaction score
United Kingdom
Hi, iv recently bought a vent axia piv unit. Iv noticed there is a space on the unit where a plug goes possibly for controls. The problem is I cant find any controls for it online, I wondered if there was anyone who could point me in the right direction, or if its not for a controller then possibly tell me what it is.

Thank you


  • 20211121_104921.jpg
    212.7 KB · Views: 148
Sponsored Links

Although I do not know anything about this unit, I did have a quick trawl of the internet!
...and like you, have not come up with any answers to what the socket does.

I have seen mention of a humidity sensor, but I don't know where that would connect.

I strongly suspect, it may be something like a serial/USB port for updating, troubleshooting, assisting install, or downloading the report logs, but that is a complete guess.

Possibly moving this post to the 'Plumbing and central heating' section may attract the attention of a ventilation installer? :)
Sponsored Links
If you look at the picture of the unit at the start of the install instructions it only shows one socket above the mains outlet. The only mention of 2 sockets that I can see are on page 5 where it mentions installing a heater. My conclusion was that it is something to do with fitting a heater. The only other thing I can think of is that it is something that had a use but is not now on new models.
Hi, I'm sorry for the REALLY late reply , just wanted to let you know I'm still none the wiser as to what that small socket on the unit does ‍♂️. Thanks for you time guys
Hi, I'm sorry for the REALLY late reply , just wanted to let you know I'm still none the wiser as to what that small socket on the unit does ‍♂️. Thanks for you time guys
Hi Mike

I came across this thread as I'm trying to source this exact plug.

It's for a manual boost control p/n 411150
Wiring instructions are on page 10 of the manual

I'm looking to make one myself as I think the price for this simple cable is a bit on the high side. I notice someone on Reddit was also asking after the connector name, with no luck
I'll be sure to update you if I find out more.
It looks like a normally-open (obviously) circuit across two of those four pins, when the circuit is closed the unit goes into boost mode. In programming you can set the boost overrun time 0hr, 1hr, 2hr, 4hr, 8hr.

So you could wire a simple light switch to this and have overrun on 0hr, meaning the unit will boost when the switch is on and return immediately to trickle mode when the switch is off. Or you could wire a doorbell button to it to activate whatever overrun time you set in programming.

Quite handy to have but I'm not paying £100+ for that. Bit more info here, but they're getting into a more fancy Zigbee set-up

The OP in that thread was able to bodge a connector but mentioned he thought the proper connectors were JST-GH. That can't be right as the pitch (distance between pin centres) on those connectors is 1.25mm and I've measured the Vent-Axia ones at 2mm...
Pitch 2.jpg

Some more close-ups of the sockets...

4 Pin - Front.jpg
Both Sockets - above.jpg

I've done a fair bit of Google-Fu this evening to find the connector. The JST-PH (shown on the right in the below picture) has a 2mm pitch but the connector shape looks quite different and there is no top-latch variant. The connector on the left is the Seeed Grove and looks close enough for me to chance around a fiver for a pack of 5 plugs with 50cm tails. If it's not quite right I'm sure a fresh Stanley blade will make it so.


Link to pack x5 50cm plugs 50cm isn't going to get me from the PIV unit to where I want the switch to be but I'll splice it onto whatever 2 core I have lying around. 0.5mm² flex would be fine.

I've topped my shopping list off with a branded Vent-Axia boost switch for a tenner on Amazon. Like I say, you could use a basic 1 gang/1 way light switch but this one looks the part and will help convince her I've done it "properly", since this will be the only bit on show.

I just need to find out which of the 2 pins of the 4 are used but I will just cross my fingers and bridge them till the PIV kicks into boost. It begs the question; why did Vent-Axia use a 4 pin connector here? Possibly something better was planned, I think a remote programmer would be amazing because climbing into the loft to make changes is a proper pain. I cannot find any hint that such a thing is/will ever be available though and I hate to think what the price would be if they want over £100 for a simple button and lead, lmao.

The more likely reason is they didn't want people accidentally swapping the heater (240v) and boost (volt-free) plugs.

I won't have time to do this for a couple of weeks so I suggest people hold tight on buying any of the parts I listed, just in case they're wrong. Will report back whether success or disaster.
Links in this post may contain affiliate links for which DIYnot may be compensated.
The Grove connectors arrived today and they do fit, bit of a squeeze as the top latch interferes slightly with the edge of the aperture but I think it will work.

Finally got time to wire this up and test it. The outside 2 pins are the ones to use (pins 1 and 4, black and yellow on the leads pictured above). Works perfectly and saved a fair few quid compared to buying the official kit.
Found this thread last week and ordered the Grove cable but also some JST-PA connectors. Took the wires out of the Grove cable and put them in the JST-PA connectors and they fit perfectly in to the vent axia unit. They're pretty much the same as the grove ones but the latch is smaller.

I've opted for a basic switch in a simple plastic box that's accessible from the loft hatch, I've just laid 300mm of insulation that I wasn't going to pull up to fit a boost cable!

As above, pins 1 and 4 are what you need.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links