Boiler modulating up and down

[pls1]

I've noticed recently that once the CH is nearly up to temperature, the boiler flame modulates up and down over approx a 30 second cycle. Eventually the boiler will switch off as normal once the room stat indicates its up to temperature.
Is this a sign the system is sludged up and needs a power flush?
I recently fitted a Magnaclean and dosed the system with X800 which got rid of quite a lot of iron oxide initially (slowed down now).

Ferroli Tempra 30 system boiler - S Plan
12 cast iron rads (no TRVs), 5 pressed steel rads (with TRVs).

 

[Dan Robinson]

Not sure whether or not you are surprised a Ferroli boiler works long enough to modulate?

Or that you think the boiler should blast at full output regardless of system load?

Either way... boilers are supposed to vary their output depending on what is needed from for the system

 

[ianmcd]

when you say "dosed the system with X800" hope you dont mean you have added X800 and left it in there and you are hoping that cleaning the magna clean will remove it ?

 

[pls1]

Not sure whether or not you are surprised a Ferroli boiler works long enough to modulate?

Or that you think the boiler should blast at full output regardless of system load?

Either way... boilers are supposed to vary their output depending on what is needed from for the system

Haha yeah - did hear that Ferroli's have a pretty poor reliability history.
This one is approx 8yrs old I think.

I know the process of modulating but this ain't normal, modulating up and down constantly every 30 secs.

 

[pls1]

when you say "dosed the system with X800" hope you dont mean you have added X800 and left it in there and you are hoping that cleaning the magna clean will remove it ?

No, plan is to drain down and refill and add inhibitor but given the issue above I wonder if it needs a powerflush rather than simple drain/fill.

 

[Boilerman2]

The Ferroli is a low water content boiler - so why do you think that the burner modulation is abnormal? sounds about right to me - oh and I too am suprised that the boiler is working long enough to reach temperature!!

 

[ianmcd]

when you say "dosed the system with X800" hope you dont mean you have added X800 and left it in there and you are hoping that cleaning the magna clean will remove it ?

No, plan is to drain down and refill and add inhibitor but given the issue above I wonder if it needs a powerflush rather than simple drain/fill.

You shouldnt leave X800 in the system if you wanted to leave it in you should have used x400, the X800 is extremely aggressive and should be used with a powerflush machine and flushed same day, you might be lucky and get away with it but you may have damaged your boiler already by leaving it in Im afraid