Vent Axia bathroom extractor fan

[NEV]

Gents;

I am hoping there is someone out there who will be able to shed some light on the following;

A client asked me to replace a bathroom extractor fan as the other one was burnt out. All the wiring was already in place and i carried out the normal tests on the circuit prior to installing the new fan. The fan was wall mounted and was a nightmare because the cotttage has no cavity walls and no loft space so i couldn't see or find the junction box to see for my self how the junction box was wired. The bathroom was fitted with Downlights which were 230/12volt the light switch was a dimmer. The 3 pole isolator was a pull cord and on ispection was correctly wired with 3 core and earth. The fan was then wired using the instructions however when turning the lights on the boost facility would not kick in. Even though there was power in the LS conductor. The van was fitted with a timer and a humidity stat everything i tried still couldn't get the fan to boost when the lights come on. The fan would run on a constant trickle but that was it. Only when i inserted a jump link into the Boost bi probes would the fan boost then it was constant. I thought it may be the dimmer switch so i changed it for a normal light switch still no boost. When the light were off the reading at the fan were 230 when the lights came on the reading was 12volts. I was thinking of inserting a seperate circuit so that he lights and the fan were operated by their own independet switch. Any feedback would be greatly appreciated i may be missing something simple here i usely only fit timer fans.

Many thanks

 

[Guest123]

Some clarification needed before anything else.

1. Is the boost function not controlled by the built in humidistat
2. How are the ELV spots wired i.e a transformer each or multiple lights per transformer
3. Is there definitely a permanent line, switched line & neutral present at the fan

Sounds like there is a problem with the SL to the fan but need clarification first.

 

[NEV]

1. The boost is controlled by the Humidity timer and does kick in when the stat is set to its shighest setting.
2. Each ELV downlight has its own seperate transformer
3. I have tested both line conductors at the fan connectors. The permanent has a 230volt reading and the LS will only give a reading when the light switched is operated which is correct however when i check across both conductors the reading will alter from 230/ 12 volts when the lights are turned on.
I thought that maybe because the fan was on constant trickle this would cancel out the boost function until the humidity rose and then the humidtiy stat would kick in and boost. However on turning on the shower and letting the humidity rise in the bathroom the boost still didn't kick in.