Myson Apollo 40S boiler keeps shutting out!

[Kav69]

when I switch on the boiler (it's usually switched off when hot water is not required as the fan is noisy and goes on my nerve!) from the main, it works for a while just fine and when water temp reaches to some level (this differs from time to time and my guess is that it depends on the temp of water because the timing each time is different) it shuts itself down and fires up again within a 1-4 seconds. From this point it works for a very short time say about a minute or two and then shuts off and so on. I have replaced the thermostats (High, Low and limit) but nothing changed!
Pump seems to be working just fine and I've already clean the system with Fernox and drained the system so I wouldn't think it is circulation. (I might be wrong though!)
Any comment will be appreciated

 

[REDSAW]

diverter.
time for a new boiler. 15 year old
has the boiler been serviced=lately?

 

[Puddle]

Well you probably hit the nail on the proverbial in your first line
The fan is noisy, thus possible cause, when fan gets hot slows down and deactivates air pressure switch turning boiler off, then cycle continues, new fan and air pressure switch required
ps when you get sorted only have on low stat setting due to age
But as Redsaw says Boiler is getting old now ,so if you can afford it ,maybe time to replace

 

[Kav69]

Thanks for the tip. Well, can't afford a new one now. But I'll fiddle with the fan and the APS and see how I get one.
Any idea where I can get a cheap fan?

 

[Kav69]

I have got it! It was actually the APS which was faulty. Replaced it and life became sweet again!!... it's sorted.
Thanks to everyone who replied to my question.
Cheers
Kavous