baxi 105 he

[buckley plumb]

been to baxi 105 he today .when switched on the flame failure light and fan light flash,
checked primary sensor and get 15 k ohms / contonuity on flow sw at pin 7 and 8 ok /no 240 volts on pin 5 and 7 at a2/ linked pins 6 and 8 on a2 to eliminate air press sw.still after reseting pump runs then instant flashing flame lock out and fan lights .i am thinking pcb now any ideas

ant

 

[Billy Bob Bob]

ap switch,common failure,when you linked the pins did the fan run?

 

[buckley plumb]

no fan even with pins linked .

thanks ant

 

[buckley plumb]

what is the third wire for on the air pressure switch. A2 pins 6 and 8 are the switch whats the other pin9

ant

 

[gasmarc]

if you reset it and it is going directly to flame failure is the fan running is there gas ?

 

[buckley plumb]

ref above . followed baxi fault chart pump running then straight to lock out and fan light flashing on flow chart it says go to D which says check flow micro sw which i did and ok - check temp sensor which was ok / and check terminals 5 and 7 on A2 for 240v if no voltage pcb. i checked all this and more .spoke to baxi tech who said link pins 6 and 8 on A2 to bypass air press sw and see if fan runs then - it did not so they agreed pcb gave customer price and she said leave it. had call of customer tonight saying she called baxi and they replaced air press sw and boiler ok now and thinks i was trying to rip her off- my question is why would baxi agree and tell me to short the pins to test the air sw and agree pcb -thinking about it now the pcb must see a normally open air press sw before the fan starts then once fan runs it must see the sw close - so why would shorting 6 and 8 make the fan run (which it didnot when i shorted with a link).

anyone good on explaining how the air pressure sw works and how to short out to test fan- was i told right if so why didnot fan run

thanks ant

 

[Blackcatgas]

the fan must run first to activate the air pressure switch, thats what those 2 tubes are that come off the fan, the fan runs which sucks down those tubes which lifts the switch in the air pressure switch.

 

[Blake]

The pcb waits for a signal back from the AP switch to say all is ok. So assuming fan has activated the APS as Blackcatgas said above, this would then allow the boiler to fire up.

Shorting the terminals by-passes the ap, or rather makes the pcb believe the APS is activated and is working ok.

As Gasman said, the APS is a common fault on this boiler, a simple continuity test will normally confirm if the APS is faulty.

Don't beat yourself up over it, it's all part of the learning process. Manufacturers tech guys are not always right, but they often know common faults on their boilers that are not printed in the manual fault finding guide.

 

[buckley plumb]

the fan did not activate so am i correct in thinking the pcb needs to see the aps normaly open first before fan runs (so if i linked the terminals 6&8 before the pcb had read the aps normaly open would this of effected the test of the aps). the boiler went straight to lock out and fan light flashing no voltage to fan.for next time are these the correct pins to link to test the aps and get the fan to run and if so why did the one i tested not run when linked out.


thanks ant

 

[Blackcatgas]

Disconect the aps wires, the fan should still run, did you test for 230v at the fan?.
BTW the 105e is an excellent basic boiler for learning the basics of fault finding.

 

[Billy Bob Bob]

just stick a aps in fault sorted i have replaced loads with the same symptoms

 

[Blake]

Baxi did put one in mate the OP said and it did fix the problem. The OP is just wondering why baxi tech told him PCB and then they fitted a APS which made him look bad in the customers eyes.

 

[Billy Bob Bob]

because there are some right dicks in baxi tech,sorry darryl had not seen the previous posts,to answer the op,s question 3 wires on the baxi 105 he,live out to fan from pcb and to aps from pcb switch wires,from memory third wire has some link to the dhw thermistor on the 24 he there are just 2 wires brown on pin 27 black on 31 so being 2 wire easy to prove will be the same on 105 he link brown and black,fan should run and ignition take place

 

[buckley plumb]

thanks to all. i will know for next time

thanks ant

 

[buckley plumb]

does the above apply to most aps and is it the common and no switch to link or nc.

i am still confussed why the fan did not run when i shorted the aps at the pcb on pins 8 &6. as most have said shorting here the fan should have run but it didnt

thanks ant

 

[Plumbcrazy56]

I always keep a working second hand aps on the van for exactly this kind of fault. I then get the new part and keep the old one for the next job.

 

[gasmarc]

regarding what baxi said Buckley you wont be the first or the last to go down that road. If you can imagine some of these people in their call centres are just reading what is in front of them and have no hands on experience, I have heard on good authority about an experienced engineer replacing 3 out of 4 pcbs on a vailant only for all the boards to need replacing again and the gas valve Ouch

 

[buckley plumb]

been to a halestaed ace today with same symptoms as the baxi pump runs but no fan- the pcb switches the neutral to the fan so there is 240 volts to the fan and back to the board and then the board switches the neutral to complete the circuit.i tested the aps off the boiler open circuit and then suck on hose closed circuit so all seemed ok - talked to tech who said like baxi short aps out and fan should run - shorted with no joy so thought pcb but after the baxi i thought i would try again - phoned tech again and got an engineer who knew from hands on- he said shorting the aps would not work as The pcb looks for and open circuit aps and then fan runs and when the aps switches to nc the fan will continue to run if it sees a closed circuit no fan - he said the only way to trick the pcb would be to unplug aps and then start boiler then short it out once boiler starts.

ant

 

[gasmarc]

hi Buckley there is a few people here who know these inside out, its a live that switches to the fan i suspect from the board not the neutral but i maybe wrong

 

[buckley plumb]

i phoned baxi today to just clear my mind and spoke to someone who seemed to know what they were talking about - they said to test the aps on the baxi turn boiler off and link the black and brown wires pins 6 and 8 but disconnect the blue wire pin 9 this will short the aps thats why the fan did not run when i tested it as told by the other baxi tech guy. but he never mentioned which terminals were nc and no . i feel better now .once bitten twice shy i will no next time.

thanks ant

 

[buckley plumb]

halestaed assure me the fan has the neutral switched .

ant