Bioler won`t shut down

[malc]

Hello, I have been to look at a system where the boiler seems to be ignoring the room stat,and going on getting hotter and hotter.Eventually the customer says she hears a strange noise from the boiler,maybe similar to a kettle boiling.
Does this sound as simple as a faulty room stat (honeywell) not sure which modal.
If it is a new stat required,do I need to know exactly which modal ?

thanks.

 

[buryboy]

You don't say whether with external controls still conected to the boiler, it closes down when boiler's own CH stat is turned down low?

Without knowing what external controls are fitted. I've presumed that there is a roomstat and external clock controlling the boiler's on/off's etc.

First I would uncouple the Clock/roomstat's wiring inside the boiler. Put a link in its place.
With this in place boiler will run independently of external controls. (24/365 if you let it).
The boiler should now only operate to the boiler's own controls.

So if you turn down the boiler's CH stat, the boiler should react to this and close down when it reaches the temperature you've set it to. Also by increasing the CH stat the boiler should fire up until it again reaches the desired temp. So whilst the CH stat is set at a high temeperature setting and with boiler running, if you turn down the CH stat this should immediately close the gas valve so the burner goes out and after a couple of mins the fan and pump stop.

If it does this, then the boiler would appear to operate properly and there is something then wrong with the external controls.

But if the boiler still keeps firing and gets hot when the boiler's CH stat is turned almost off then something inside the boiler is the problem.

 

[malc]

could it be a motorised valve problem ?

 

[BLOD]

Could be a stuck microswitch inside the motorised valve giving permament power to the boiler.

Hope this helps

Blod

 

[GrahamM]

With BLOD on this one. Quite a common fault. Would rule this out first before looking at controls.

 

[malc]

thanks for the answers guys, went to follow up and customer says that after my bleeding a couple of rads and turning the room stat up and down a few times ( she wasn`t aware of the room stats function ) the system seems to be ok now thank you . so will have to wait till it fouls up again in order to trace the fault

thanks again.