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DIY Forum >> Plumbing Questions >> Baxi combi instant 105e flame failure
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Message started by bris on Apr 2nd, 2008, 9:18pm

Title: Baxi combi instant 105e flame failure
Post by bris on Apr 2nd, 2008, 9:18pm

Hi I have a baxi combi instant 105e which when turned on goes to flame failure almost instantly. Ive managed to eliminate the pcb as the problem so took it apart to see if the fan was working which it was. While the cover was off the boiler worked with no problems. When i put the cover on again it still worked but when I tightened the screws to create a seal in the chamber it cut out and stopped working again. loosen the screws again and it works again possibly letting some air in keeps it working but again tighten the screws and fails. Hopes this makes sense to someone and maybe someone has hsd a similar problem, thanks for looking.

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 2nd, 2008, 10:58pm

make sure the flue intake is clear check the venturis follow the 2 silacone tubes from the air presure switch to the flue remove the tubes those are the venturis inside the flue make sure the heat exchanger is clear and not part blocked so as to stop the poc,s going through and clearing have seen this befor its usualy due to lack of servicing

Title: Re: Baxi combi instant 105e flame failure
Post by bris on Apr 3rd, 2008, 12:14am

Thanks for the reply lovejoy but it was serviced around 4 weeks ago when and the the guy striped it down and cleaned everything out. I took it apart and checked just to make sure though. Any other suggestions appreciated.
thanks

Title: Re: Baxi combi instant 105e flame failure
Post by thescruff on Apr 3rd, 2008, 12:17am

Yes get the guy back out, you really shouldn't be playing with the combustion side

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 3rd, 2008, 9:10pm

thescruff is correct, i stil think its down to the flue double check all flue connections next the air presure switch, as it worked sinse service if not has he got the tubes wrong way round on air pressure switch

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 8th, 2008, 8:57pm

Hi bris I have the same fault started 2 days ago , straight to flame fail only after a reset and the conbustion door loosely on will I get a flame,
so far new air stwitch £18 and new fan £ 75 still the same fault ,baxi say check flue etc !! done all that, it it pcb !!! but how does it know the door is letting in more air??? Gas valve ??? but it is lighting up ???
please let me know how you are getting on

Title: Re: Baxi combi instant 105e flame failure
Post by watty on Apr 8th, 2008, 11:20pm

hi richrtr. i'd say a pound to a penny its a dirty venturi,(in the flue elbow wher the two rubber pipes from the airswitch go to).when you loosen the cover you allow more air in to the chamber increasing the flow through the venturi. got to be that unless you have crossed the pipes when you put the new airswitch in :)(just checking).

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 9th, 2008, 5:03pm

Thanks very much for the reply, when I fitted the new fan it was the cowl and all,,,, so new clean venturi plus pipes and and aps, I have a complete one year old 105 for the doner for parts, just get her going for the mrs to have a shower again by letting air in..... via the combustion door, dont want to change the gas valve unless I really have too, but running out of ideas, could the gas valve be sticking????? and cant open against air pressure from the fan, with the door open air pressure less and valve can open ????

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 9th, 2008, 5:38pm

nope this is a negative presure boiler, eaven if it was only a 1 year old dona id check the venturis its not the gas valve at all its somthing in that combustion chamber thats for sure

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 9th, 2008, 5:45pm

just a thort now dont all laugh never seen it never tryed it but have u got the wires on the fan the rite way earth is easy but L and N if on wrong spades would the fan run wrong way lol dunno as i say

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 9th, 2008, 6:03pm

Checked fan cables via wireing diagram its ok!
as I am getting the spark with the door fully closed , surly I am proving the APS and fan as it going throuth the ignition sequence ? all I am then doing is allowing more air in getting the flame on then fully closeing the door , runs fine untill call for heat cancells then will not restart. All I have not changed is Pcb and gas valve. there is 230 v goes to gas valve so pccd must be ok ? is it the gas valve ?

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 9th, 2008, 6:37pm

it is nothing to do with the gas valve as it wouldnt run with case cover off if it wont when on, the gas valve dont know u have the cover off, the fault is deffo somthing inside the combustion chamber u sure the fan is totaly free and running to speed check wires on aps commen  no & nc

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 9th, 2008, 7:12pm

Many thanks for your paitence, yes the fan seems to be running a full speed, the boiler its from was fully working when removed, it had only been fitted for a few weeks last year. so I must belived it ok and the aps too I,ve checked the venturi its clean. whats the chance of this fan and venturi beeing duff and my one? my boiler was good for 4 years before this fault, servied and cleaned every year. The baxi fault chart also says 230 v at gas valve yes = replace gas valve.

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 9th, 2008, 7:27pm

says  PCB- A1 connector has 230v ac across terminals 2 & 4  = yes replace gas valve that is when no gas at burner if not 230v and no flame faliure flashing replace pcb

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 9th, 2008, 8:17pm

So are we saying replace pcb got one shall I fit it in the morning wife is moaning that its cold!!!!!

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 9th, 2008, 8:19pm

More to last,,,,,,,, but I am getting the flashing neon light,,,,,,,,,,,,,,, and I,m pulling out my hair================ come on the Bris how did you sort it ???????????? :-?

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 10th, 2008, 7:04am

no im saying do those  tests to prove its not the gas valve, a dry joint on the board ? mmm how dose the board know when u have opend the chamber i still think its somthing in that combustion chamber, i have fit boilers from the box and aps dosnt work, the diaphram is moveing with cover off but not with it on i would deffo invest in a new aps for this boiler and double check tubes are rite, if the gas valve or board had gone it wouldnt work cover off or on, its you alowing air into it thats making the diffrence

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 10th, 2008, 7:11am

thort , is the dona boiler a 105 he by any chance ?

Title: Re: Baxi combi instant 105e flame failure
Post by richrtr on Apr 10th, 2008, 12:33pm

Thanks Lovejoy for all the help but fingers crossed I think I have sorted it!!!!!!!! Was about to change Gas valve as per book earth wire then pressure sensing pipe.... Followed that up to the brass conecttion in to the combustion chamber and then gently blow and sucked up and down it!!!! then went to doner boiler and did the same ...wow there is a diference in the amount of pressure that could be sucked down the clear pipe .S o changed them over and ,it now fires up with the door fully fitted. The newer one is a slightly different design ????
So did it wear or is the gas valve getting on abit four years and its tolerance for that in put from the pressure sensing pipe is a bit out. I wonder if changing the whole G.V would have did the trick. Fingers crossed now its ok. :D :D

Title: Re: Baxi combi instant 105e flame failure
Post by lovejoy on Apr 10th, 2008, 3:03pm

as i sed at the start down to servicing that tube should be cleand with a air duster at each service glad its sorted was becomming a saga lol

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