myson fanfare 15/30 overrun problems

[moby]

Hi, Yuor help please, my son has just moved into his first house and already having problems with the boiler, the boiler is a myson fanfare 15/30 with a honeywell st600 24 hour timer, problems are that the pump seems to run continuously and does not turn off when water has cooled down or even when the timer has clicked off, it also has a habit of starting up of its own accord. I have got a wiring diagram which shows a overrun thermostat with three terminals but the one on this boiler only has two. also not sure if this is a new problem or maybe it is not wired correctly. I would appreciate any ideas.

 

[mcguire]

sometimes only two are used. just like a switch. It probably will be the pump overun stat. it will be stuck and permanantly in the closed position. You will need a heating engineer to change it for you. The way to prove this is to check the resistance across the two terminals. if the resistance doesn't alter when it is cold to hot then its the switch. Readings will probably read O/L (normally open) or about 1.9ohms (normally closed)

 

[moby]

Mcguire,
I will check it out. I forgot to mantion that while I was having a look the other night that even though the timer was set to off the fan would occasionally start up on its own is this normal, I am not used to these new boilers because mine is one the simple cast iron variety!
Many thanks Moby

 

[ChrisR]

the fan would occasionally start up on its own is this normal

No!