Main 24HE flame failure

[dc84]

Hi went to a Main 24 he today (very much a B rated baxi combi HE)

Boiler works fine 50% of the time. There is a fault on CH & DHW mode which is as follows;

Pump runs, primary flow swith operates, fan runs at full speed but there is no atempt at igniton, then flame failure light comes on, will not reset, you have to turn selector swith on/off a couple of times. or;
When the boiler is fired up in either CH or DHW mode the flame will cut out then straight away fire up again and carry on working.
I have had this probem with the baxi 105he and it was the pcb, i keep a selection of pcbs in the van so tried it on this and it hasnt sorted it.
Im thinking check min burner pressure, air pressure switch (unlikey as it does fire up most of the time) flame sensing electrode.

Any iders?? Anybody come across this probem before??

Will be going back to carryout more checks so will update
Cheers!!

[Toddyplumb]

Try that air pressure switch. Had it a few times right on the edge of its pressure setting (tiny hole in diaphragm) just creeps off

[dc84]

I see what you mean, just enough for the boiler to cut out but not enough for it to not work at all.
I'll update and cheers for the reply!

[REDSAW]

weve had 3 new pcb's on these boilers a few times now, try another.

[gas man]

could be airswitch had a few go on the main,pcb tends to give the same fault but they are not weak boards

[dc84]

Went back and replaced the air pressure switch- Sorted it!

I noted in the manufactures instructions it says to take the fan out first in order to get to the air pressure switch (HE model) I just loosend off the side panel and got my hands in there, a lot quicker than taking the fan out!!

Good diagnosis guys, and thanks for the replys!

[martin1234]

pls help. my baxi 24 he burner fails. cannot get it to start up. i am not a plumber unfortunately but would like to see if i can try to rectify the prob with your help

[gas man]

pls help. my baxi 24 he burner fails. cannot get it to start up. i am not a plumber unfortunately but would like to see if i can try to rectify the prob with your help

check your condensate pipes not frozen if its a he model

[gasmarc]

a nice kettle of hot water on pipe should do it

[martin1234]

check your condensate pipes not frozen if its a he model

thanks for your reply. it fails intermittently! works then stops. it has been doing this for few weeks now

thanks

martin

[gas man]

probable ap switch failing