Help from a break down guru with potterton kingfisher mf 80

[clemda1]

hia guys,

Called out to a king fisher this evening hoping someone can help.

Problem:
Boiler not firing.

On arrival found redlight on reset called for heat. Fan engaged but no ignition. Took cover off tested for 240v between live and switch - ok. Called for heat again fan and pump engaged boiler fired nice blue flame for 10 mins.
Put cover back on, retested but again no ignition however fan still running. Pried cover open slightly then boiler fires and stayed on.
I'm think it's an air flow issue but looking for advise as to how to narrow it down.
Venturi or APS or Fan?

Thanks in advance for your assistance

 

[ShaunCorbs]

will it run with the cover off if yes you have a blockage in the air side of the flue

 

[Gas74]

Could be a corroded inner flue. Very prone to this.

 

[Harvest Fields]

Are these the ones with the flue stat?

 

[Gas74]

Pcb also very common

 

[Gasmk1]

Air pressure switch

 

[clemda1]

will it run with the cover off if yes you have a blockage in the air side of the flue

hia shaun,

thanks for the reply,
yes it only runs with the cover off. can you be a little more specific regarding where the blockage may be... it's an open vented system so when you say air side of the flu do you mean the inlet via venturi? or inlet vents at the top of the boiler where the flu is? sorry new to this fault finding malarky and this is the first open vented system ive worked on...

 

[clemda1]

Air pressure switch

hia gasmk1,

thanks for the reply, if it was an APS fault, would it not fail to run regardless of cover on or off? given that the pcb could not prove air flow?

 

[clemda1]

Pcb also very common

hi gas 74,

can the pcb tell if the cover is off or on with these older boilers? i only ask as it only works with the cover off?

 

[clemda1]

Could be a corroded inner flue. Very prone to this.

could you please explain how this would cause it to only ignite when the cover is off?

 

[clemda1]

Are these the ones with the flue stat?

had a look at the manual cant see a flue stat but there is a ttb stat/interuptor.. but i think these detect incomplete combustion...given it runs fine with the cover off dont think this would be the cause

 

[jtsplumbing]

More likely fan is running to slow,

 

[ShaunCorbs]

hia shaun,

thanks for the reply,
yes it only runs with the cover off. can you be a little more specific regarding where the blockage may be... it's an open vented system so when you say air side of the flu do you mean the inlet via venturi? or inlet vents at the top of the boiler where the flu is? sorry new to this fault finding malarky and this is the first open vented system ive worked on...

Flue, check the air side of the flue is clear then move to other things like fan rpm etc

 

[Last Plumber]

Clean the Venturi on the fan, check flue integrity, check fan blades are clean, check fan speed, test APS.

 

[mfgs]

Fan running slow, venturi blocked, APS is failing or an air supply problem with the flue.

 

[RoryD]

Clean Fan Blades and venturi - tiny barnacle like residue will stop operation socarbon strips are good for this. Ensure fan turns smoothly. Check APS tubes for wear/ cracks. Heat exchanger clear? If all well and it fails it'll be APS.