Boiler fan keeps running

[JayPage]

Hi all, my grandad gave me a call and asked if I knew why he's boiler fan kept running with no demand. As the insides of boilers are not my specialty I thought I'd ask you nice chaps on here. He's got an older style greenstar junior, probably around 8 years old. I said it could be something to do with the pcb but I'd be guessing if I'm honest. Any help would be great and just to recap there is no demand nor has the boiler been used to bring the fan on. I don't think he's boiler has the capability to pre heat the domestic exchanger either.
Cheers in advance

 

[joe-90]

Mine does this sometimes and as far as i can tell, it's when there is a sudden drop in water pressure tripping the pressure switch fooling it into believing that there is a demand.

(now you'll get an answer)

 

[Boilerman2]

And there was me thinking that it happened when the wiggle pin got stuck!!

Some older permanent pilot type fan flued boilers ran the fan at low speed when there was no heat demand not sure about your Workchester as I don't get to work on too many of those (thankfully!!)