Advice on setting up humidistat bathroom fan correctly

23 Jan 2012
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United Kingdom
Hi there.

I had a Silent Tornado ST100HT put in on Friday evening by my electrician:

I specifically asked that the fan was not connected to my light switch - as such, the humidistat only comes on when humidity levels reach beyond the set level or you pull the cord (which sets the timer running for 20 minutes, regardless of humidity).

I did not touch the humidity level on the fan, so it was put it in at its default (and lowest) level of 60%.

Since then, the fan has run continuously.

According to this (point 6):

" It is also important to note that when a humidistat fan unit is first installed it can run continuously for a few days as it settles into the new environment."

I suspect that something is now wrong as it has been over three days, now.

It may well be that my bathroom is consistently over 60% and will therefore never turn off.

Is there a suggested way of getting humidistats to the best level? I was thinking of turning the humidistat to its maximum (90%) and perhaps turning the dial back a tiny bit each day until the fan comes off and on - which is going to be very tedious to get right.
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My house shows around the 55 to 65% old house 65 to 75%, father-in-laws house 75 to 85% I would say 60% is too low.

However if the sensor becomes saturated it takes ages to dry out, so set at 90% the room is more like 100% before the fan starts, so then the sensor is very wet, so takes ages to dry.

I personally gave up with humidity sensors, colder it is outside the lower the humidity, so it seems you can never get it right, get it working A1 in winter and always running on summer.
Turn it whichever way it needs to go to make it go off and start from there.
Thanks guys - annoyingly, the instructions state that you must not adjust the sensor while it is powered on.

Really irritating as I could have otherwise bought a humidity sensor off E-bay and tried to match it to that.
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Pull the breaker for the circuit that controls it, leave it a couple of minutes, power it up and see if that works. It has been wired up correctly hasn’t it?
Pull the breaker for the circuit that controls it, leave it a couple of minutes, power it up and see if that works. It has been wired up correctly hasn’t it?
Thanks for that - I shall try turning off the power. Whacking up the humidity to 90%, leaving the power off for 30 minutes or so and see what happens after that.

I am pretty sure that it has been wired correctly (used a reputable electrician).

One odd thing, I have noticed is that the site:

States that the overrun timer can be adjusted, as well, but there is only an adjustor for the humidity - really confusing. I hope that that is a simple mistake on the website.
Well there should definitely be two adjusters inside unless the wrong model has been fitted. A picture of the innards would confirm.
Yep - had a look and there is only a single dial for humidity only (top left of photo). Nothing for adjusting timer, which is odd.

I have fitted a handful of humidistat fans on perm live only. I have never used your brand but I have had problems with the Vent Axia one.

It would run even if it was raining outside.
Thanks for that - I have since turned the extractor fan back on (with 90% humidity start up) and it has not once turned off. The room is completely dry and I even used a VAC condensation vacuum to make sure.

It is really wet, outside, which might be constantly triggering the humidistat. If that is the case, it is not going to be much use over the winter - constantly sucking the (very expensive) heat out of the house.

I am coming round to the idea that humidistat fans are a bit pants - might have to consider one with a pull switch and timer instead.
My fan (in the upstairs) bathroom has been very reliable, but once every blue moon it kicks in (will try to find the model number). my downstairs bathroom has a much. much more expensive and larger diameter Icon fan. That has the module with a PIR, over run and humidistat. It often kicks in unexpectedly, but I am not sure if the PIR sees dead people or if it is the humidistat kicking in.

I initially opted for humidistat fans because no one turns the lights on if they are showering when it is light outside.
I initially opted for humidistat fans because no one turns the lights on if they are showering when it is light outside.
Exactly the same, here.

We have a big window in our bathroom, so showers in the morning do not require a light on.
I have 2 of these fans fitted, both had PCB issues and eventually they sent 4 of them as a sorry.
I use separate sensors and measure my whole home for temp and humidity in each room to ensure I have my low temp heating balanced (so far each room is within 0.5 of a degree and within 10% humidity )
I have the fan operate full blast on light switch and then its around half speed after 20 minutes but this continues pretty much 24/7 with the humidity setting.
The shower was last used at 7am and now (16:00) its still showing 66% humidity.
In experience, <60% humidity in any of the bathrooms at any time is impossible to achieve
I just accept that the fan operates 24/7 but I also have it wired so that I can switch it off should I wish to do so

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