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Hi guys bosch 24i junior,model before greenstar,turned on call for heat or hot water fan will not fire up,blow down tube on air pressure switch ,fires up straight away,am i right in thinking that on this model the air pressure switch must be in closed position at rest to start ignition sequence,thanks rob

Fan running ? operating the air pressure switch makes the boiler come on - this is what the fan should do.

If the fan isn't running is there power to the fan ? if yes - replace fan.


htg

[quote="htg engineer"]Fan running ? operating the air pressure switch makes the boiler come on - this is what the fan should do.

If the fan isn't running is there power to the fan ? if yes - replace fan.


htg[/quote] hi htg no fan does not run,when boiler turned on there is no power to the fan and eventually goes to fault flashing 4 times a second,if i reset it and blow into aps fan starts straight away,there is no power to the fan when boiler first turned on and when i manually start it by blowing aps there is only 180 volts ac to it has the pcb had it?

If there's definitely no power to the fan, then yes could be PCB fault.

However there wont be power to the fan as soon as you turn the power on, there'll be a sequence. Is the fan motor warm ?


htg

[quote="htg engineer"]If there's definitely no power to the fan, then yes could be PCB fault.

However there wont be power to the fan as soon as you turn the power on, there'll be a sequence. Is the fan motor warm ?

hi htg engineer sequence starts with pump,fan motor not warm ,no power going to it,just before boiler goes to flashing fault light board relay clicks and fan spins momentarily

have you checked the water pressure switch, they do block up and do cut power to either the pcb or fan i can't remember right now

Thanks for your comment re blowing down air pressure switch tube - you have saved me £150 for a new control board.
Thanks to you (and of course, my own genius) I have completely identified the problem on my boiler and fixed it in 10 minutes!! Hope this helps other people:

My boiler has been occasionally refusing to start in any mode for several months and a week ago it stopped altogether. I was getting the rapid flashing red light. I tested everything as per the manual, including the resistance on the air pressure switch. HOWEVER, what the manual does not tell you is how to test if the switch is closing when the boiler is on. Anyway, everything else tested OK so I was about to buy a new control board when came on this site and read all the comments. I saw the comment about blowing down the tube to test the air pressure switch and thought "that's a good idea".

SO, I disconnected the red tube from the fan and switched on the boiler supply (HW tap running to create demand). I had to blow really hard down the tube but, hey presto, the boiler lit!! As soon as I stopped blowing the boiler went off and the red light flashed rapidly. This worked 5 times in succession so it was fairly conclusive.

I then looked at the flexible pipes where they go into the switch and there is a plastic Y-junction that goes to a nipple on the top of the boiler (for air testing, apparently). This looked melted, so I pulled the tubes off and yes it was melted so that there was almost no passage left inside. I then took off the switch itself (one screw on top of the boiler casing, and looked at it. Definite signs of melting.

I then looked at the two connecting tubes built into the switch that you push the flexible plastic tubes from the fan onto.

They were almost melted shut!. I used a 2mm and then 2.5mm hss drill bit to open them out again and then re-fitted and tested everything.

Result: happiness. A perfect fix for £0!!! I can't thank you enough for your help (and everyone else on here.).

I only did this an hour ago - so I will report if I have further problems, but I have checked and re-checked it and I am pretty confident.

My only concern now is that I do not want to fit the switch back inside the boiler case (it is currently sat on top of the boiler) as it will start melting again - any suggestions?

Regards, Guy.