# Forum Home Renovation Heating & Cooling  Brivis wombat 92 central heater air fan does not shut down.

## redvl2002

I am new to the forum, any help would be great.
I have a brivis wombat 92 central heater in the roof space and fan does not turn off when the heater is turned off.
I have replaced the old controller with a new digital room thermostat, part no B021964. 
The heater seems to work fine with the new controller, but the air fan still does not off when heater is turned off.
 Thanks.

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## watson

G'day ,
There's an Installers Manual in the library.
Not sure for which model Brivis though, but it might give you a clue.

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## plum

Sounds like electronic box is faulty, gas control is alright if it's running.
Can't be 100%, unless looked at. 
Does the fan turn off in it's normal cycle, i.e. when you reach desired temperature?

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## redvl2002

It seems like the burner turns off when set temperature is met, however the fan continues to run.
Where is the electronic box? Is their a way to check if it is faulty? 
Thanks

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## plum

Depends on the age of the unit as to which box is fitted, some have green and red lights which diagnose the fault, others dont and a matter of changing box over. Again depending on the age, it will be accesible once the front access cover is taken off.

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## redvl2002

sorry to sound desperate, this problem is really pissing me off

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## redvl2002

this is wht i see when i take the cover offAttachment 89396 
Your help would be great.

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## plum

Not getting the Attachment. Any ideas Mr MODS

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## Bedford

> Not getting the Attachment. Any ideas Mr MODS

  Nope, I can't see it either in order to fix it.   *redvl2002, check the notice at the top of the page and upload pics as it says please.*

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## redvl2002

Here is the pic again. 
I appreciate the help.
Thanks again.

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## plum

Quite an old wombat, between 20-30 years old, firstly the white button protruding from the browny coloured box has manual and auto fan control. make sure it's set on auto, pull it out for auto. That may be the issue.

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## redvl2002

I've tried that mate, do they ever get stuck?

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## chrisp

If it is one of the really old units, there are two thermostats: one the control the burner (i.e. when the house is too cold, turn on the gas).  The other is the fan thermostat (i.e. when the burner is hot, blow air over it to warm the house).  The 'fan' switch simply overrides (i.e. shorts out) the fan thermostat.  The fault may be a faulty/stuck fan thermostat.

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## redvl2002

Obviously the fan thermostat is located near the fan, what does it look like?
Could it be caused by a short in the fan thermostat wiring?

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## plum

Yes, behind that cover the white button is connected to, is the fan limit switch, it rotates as the heat exchange heats, it has 3 settings, [can't quite remember what sequence they are, but not important as yet] it may be getting stuck and not rotating as it should. Haven't replaced one for at least 20 years, but I think it's relatively straight forward.

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## redvl2002

Ill have a look tomorrow morning.
Have to pick up kids today.
Thanks again for your prompt input.

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## redvl2002

Plum if your there. 
On further inspection to the wiring inside the removable cover i found this blown, im not sure if it is a fuse or just a link?

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## plum

It is a fusible link cut-out, try bridging it out to test, not sure if the symptons indicate a blown link though. Also, if blown there is a reason it has blown, which has to be found.

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## redvl2002

Mr Plum, On looking of wiring diagram, it was a burnt out resistor 470 ohms, I have replaced resistor with 0.5W 470 ohms resistor, Is this a suitable resistor?
Fan still continues to cycle?
Should the dial with the three setings rotate when the burner is active?

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## plum

The dials' 3 settings are off, on, and off [limit], it rotates with heat expansion from the heat exchange. There is actually an American dude on youtube explaining how the fan limit switch works, worth viewing, [ I don't know how to post links, my kids wont teach me] better to watch that, than try to explain. 
It is also possible that you've got a cracked heat exchange, which is bad news. To check this, one must look closely at the lit burners on start-up, b4 the fan kicks in. When the fan starts, watch for any noticeable change in the flame characteristics, if they waver or start lifting, means that there is air being blown into the combustion chamber, which will leak c.o. through the ducts or flames could be forced out the front of the unit causing a fire. 
But without an inspection from a gasfitter, be a bit careful, in fact be a lot careful.

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## redvl2002

Thanks for your help Mr plum, its definitely the fan limit switch which was sticking. I read somewhere to give it a few good taps to make it unstuck. Seems to be working OK for now. I don't think that the heater exchange is damaged as i checked for flare ups or distortion in the flame as the fan starts.
Thanks again for your help. Much appreciated.

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