Baxi 105e combi fan flue fault flashing

[RayPlumb]

Have a baxi 105e combi. The fan flue fault light is flashing. Hot water on and fan starts and thats it, no burner. The fault finding check list says Air Pressure switch. Tested - got continuity on brown + black (boiler off) on switch... No blockages in APS pipes or flue.
Put Central heating on and nothing. The fan has a small kick probably a second of voltage to fan and that is it. Fault finding check list says micro switch/ sensor/ PCB.
Any advice appresiated..

 

[RayPlumb]

Did manage to get it working on CH for a few min until I switched it HW and then nothing at all.

 

[grahamgas]

Every 105/performa that have had this syptom it has been the PCB. Always seems to pulse fan when trying to start.

Do you get 240 to fan contacts when DHW demand?

Graham

 

[RayPlumb]

No checked again and fan not working with DHW demand. Althrough split second of 240v then nothing.

 

[SafeGasInstall]

flow switch ok ?

 

[RayPlumb]

Flow switch ok all moving as should and continuity when switched . Tested sensors 4k ohms each. Put all back and tested DHW only just in case and it worked??.. switched to CH and burner went out fan off. Back to DHW and nothing. Fan flue fault flashing as usual...

 

[mikegas]

venturi?

 

[Billy Bob Bob]

are you gsr?

 

[RayPlumb]

In training, the boss wants me to come up with a solution before wednesday when we are going to fix it. Thought I would get a heads up on solution from forum.

 

[SafeGasInstall]

and how come you were there fixing it 5 hours earlier ........do I smell something

 

[RayPlumb]

Vacant house and I have a key to finish bathroom job?

 

[SafeGasInstall]

not my business at all

 

[cadiz]

Is there 240v across terminals 5 & 7 on the A2 connector on PCB?

 

[RayPlumb]

There is a slit second of 240v to fan (terminals 5 & 7 on the A2 connector on PCB) then nothing. Almost like a little kick to the fan 1/4 turn and off.

 

[cadiz]

PCB Fault I suspect.

 

[RayPlumb]

Thanks cadiz

 

[mickie]

you'll cry if you change the pcb and it isnt that.. you have to be sure its that before changing it..

you've checked the aps ? how have you checked it

 

[cadiz]

One thing to do before replacing is to take out the PCB and look for signs of overheating on the back.

 

[RayPlumb]

The pcb was changed and works fine now.. Thanks All