Alpha he cb25 flashing a and b same time

[dougal]

hi all

just after second opinion
has anyone has a fault with a and b flashing at same time. only thing working is pump. checked continunity across low water pressure switch, continunity on over heat stat and fan stat. checked air pressure switch isnt stuck ie with no demand theres no continunity on two gey wires on air pressure switch, so its not stuck open. as theres no voltage to fan, it can only be p.c.b

dont have manual not experienced with alpha fault codes.

many thanks

 

[Linkyplumb]

After checking for restriction in flue and tubes,
Check for 24vdc across terminals 15 on plug M5 and terminal 20 on plug M6, if no voltage then pcb is goosed.
If there is voltage then check for 24vdc between term 14 on M5 and term 20 on M6, I no voltage there then pressure switch is shagged

 

[dougal]

i will check that. sure its p.c.b as no power to fan and air pressure switch is o.k as its not stuck open.

 

[Alpha man]

Fan or PCB, but do check APS!!

 

[Ermintrude]

Nope ignore me

 

[dougal]

i did check aps on first visit that it wasnt stuck, fitted new p.c.b and set up heating potentialmometer
min rate checked max b.p and rechecked min b.p all working good.
jobs good one,

thanks