Baxi 105e Flame Failure Problem

[quietman]

Hi Guys/Gals, I am having an intermittent flame failureproblem with my boiler. Problem is apparent on both heating and domestic separately so appears to be the ignitionsequence (bit of my background, time served plumber but although I’ve been outof the trade for near 20yrs I’ve kept my hand in but not specifically trainedin combi’s). Boiler might light up no problem but for example the heating mightcycle a few times (sometime for 90 minutes or so), and then fail to light, flamefailure light flashes. Same with hot water, although I have watched the burnerflame just stop and start again almost instantly before flame failure isactivated. I’ve serviced the boiler and removed and checked every injector, noproblems found. I even removed the gas cock to check for obstruction but it wasfine. Strong spark apparent when ignition starts but when I get a flame failurethe gas lights at the spark but does nottravel to the flame sensor in time or theres no gas to light at all !! It all seems to point to the gas valvesticking – is this possible? I know it could be the PCB and I’m waiting fora test bulb to check it (230v A1 connectors 2 and 4 to gas valve) but I can’tsee a PCB failing intermittently unless you know otherwise. To confuse mattersa bit more the Gas Board have found water in my service line but although theysucked it out I’m still having the problem (gutted, I thought that was thesolution). They are renewing the line tomorrow but I’m not confident that isthe problem. Any help/insight you might give me would be most appreciated.

 

[diamondgas]

Funny you mention water in the mains I was going to suggest putting a gauge on the P! test point on the gas valve (inlet pressure) thinking you may have a dodgy meter or meter governor! If you have a constant pressure on the inlet then that'll rule out up stream problems and allow you to concentrate on the boiler.

 

[Blake]

Check the Air pressure switch for correct operation, common fault on these.

 

[quietman]

Thanks for the suggestion but I'm not experienced in combi's, how would I test the Air Pressure Switch ?

 

[quietman]

Fitter changed the reulator and the meter before hearing the gurgling noise from the supply pipe. I hoped that sucking the water out would fix the problem but no such luck.

 

[quietman]

Could the pressure switch cause the problem, would the ignition sequence start if the pressure switch was not functioning correctly? Is it possible to have an intermittent fault with this type of switch. Sorry for all the questions but I'de really like to learn as well as fix the problem. Thanks.

 

[Blake]

Yes the APS can have an intermittent fault and can be tested using a multimeter. The problem I have is that you are not gas safe reg so I'm not allowed to advise you on how to test as this requires taking the cover off the boiler. Sorry

 

[diamondgas]

Could the pressure switch cause the problem, would the ignition sequence start if the pressure switch was not functioning correctly? Is it possible to have an intermittent fault with this type of switch. Sorry for all the questions but I'd really like to learn as well as fix the problem. Thanks.

quietman, I think you need to see if this fluctuation in pressure is happening elsewhere in the house. Do you have a gas hob? Turn it on then run a hot tap to light up the boiler see if anything happens. I still wouldn't rule out water in the gas main being the culprit! You need to eliminate that before you look elsewhere. It's important to know that you have a constant supply of gas at the required pressure!

 

[quietman]

I respect your position, I'll try to find out how some other way. Thanks anyway.

 

[quietman]

Last night I lit my gas fire on full with no problem and still had problems getting the boiler to light. Resetting seems to sort out the problem but only for the initial ignition. Seems to point to the boiler I think. I had pretty much settled on the gas valve but this air pressure switch suggestion has merit, I just have to find out how to test it. I am surprised that the ignition sequence will start if the APS is not operational, I see the spark and hear the what I think is the gas valve opening but no/little gas apparently being delivered. Need to search for how to test the APS. Thanks for the suggestion.

 

[quietman]

Things have moved on but not got better................

Just replaced the Gas Valve ( I convinced myself it was sticking as there was 240v acros A1 2&4), set the main burner pressure (its been a while since I used my "U" gauge, thats what we called them back in the day !!) to 13mb with both HW tap open and CH calling. boiler fired no problem, now no sign of low gas flow/pressure (??). Alls well until I shut off the HW, boiler runs for about 5-10 secs and shuts down "Flame Failure", no ther failures indicated. OK, so I run the HW a few times for a reasonable duration, always fires up and does not shut down unless I shut off the HW, great. Now I try the CH on its own, fires up no problem, now no sign of low gas flow/pressure, but after 5-10 secs shuts down "Flame Failure"
Now I can't believe its the Flame Sensor because theres apparently no issue with the HW. I'm now starting to think PCB (after busting £65 on a new Gas Valve !!), could it be some sort of modulator problem on the PCB ? I want to fix it but I also want to understand the problem.
Any suggestions greatly appreciated, thanks.

 

[GQuigley67]

believe it or not we still call them U guages lol !!

think its time to call in a gas engineer my friend, I would think its APS related not the PCB anyway

 

[quietman]

GQuigley67, thanks for replying but I'm not getting a fan failure neon and if the APS was playing up then I'd expect both the CH and DHW to be showing the same fault (please correct me if I'm wrong). I went back to the boiler later this morning and refitted the "old" gas valve. The 10 sec shutdown went away (??). With the U gauge fitted I went through the same setup checks I did with the "new" valve, DHW and CH calling showed 12.5mb. I shut down the DHW expecting the boiler to shut down after 10 secs but it did'nt !! I watched the U Gauge as the boiler heated up and observed the Modulator adjusting the pressure to control the boiler temp as it should. What I did notice was the min pressure was about 1.5mb (manual says it should be 2.5mb +/- 0.2mb). I removed one of the modulator cables and adjusted the min pressure to 2.5mb, increase of 40%. Boiler on CH only has run for about 45mins without a problem, shut CH down and tried DHW and it fires up ok. So, I now have a Gas Valve that I do'nt appear to need. I'm waiting for the house to cool down before giving the heating an extended run.
The "old" gas valve did have some crap on the filter, could this have affected the min pressure (which I have now adjusted up) and caused the whole issue ? Thanks for your suggestions.

 

[GQuigley67]

make sure you do tightness test and spray with LDF since you have replaced valve, you seem to be competent enough but its easy to forget if your not used to doing it.

the minimum pressure may have not been sufficient enough to keep the flame lit due to the filter being dirty, I'm not certain myself but let us know if problems return

 

[diamondgas]

Hi quietman...

You've done a grand job getting to the bottom of your problem. One thing about being out here is that you don't get to phyisicaly see what's ging on with appliances. It certainly sounds like you've cracked it. Low pressure can be detected some times and not other!

Good to hear you didn't give up!

 

[Poxi]

Deleted. Above post not read correctly...Sorry

 

[GQuigley67]

think the OP has cracked it poxi, he adjusted the pressures himself and seems to have found the problem fingers crossed plus I think he has kept old gas valve in situation anyway ??

would of been best testing gas valve before taking new one out of packaging that way you could have returned it, but lesson learned i guess.

Gas laws state that you can work on your own boiler as long as you are competent to do so, so you've done nothing wrong either

 

[quietman]

20.00hrs update....... Fired the heating up at 18.00hrs and just turned it off (I've lost about a stone due to the heat, wife suggests I keep it on longer), heating cycled many times without a problem. I'll only feel confident when I've run the heating on two more seperate occassions for al least 2hrs each time (I'll do this over the next few days). DH seems fine. I still do'nt understand why the new gas valve kept shutting down after 10secs but hey ho, can't believe the new valve has a problem, maybe the min/max settings needed adjusting on it as well. Anyway, although its been frustrating its nice to get the old grey matter working again, I took early retirement 20 months ago (I'm 54 so not over the hill yet). Thanks to everyone for their help/suggestions/support.

ps. do'nt know what LDF is but fairy liquid was liberally applied, could see no way of testing the top manifold connection but its not really under any pressure when gas is that side of the valve and the "o" ring looked in great shape and was correctly placed when tightened.

pps, anyone need a Baxi 105e gas valve ???

thanks again, any changes and as Arnie said " I'll be back".

 

[GQuigley67]

LDF = leak detection fluid

the new valve would of had to been set

 

[quietman]

Final update - I've now run the CH on 3 seperate occassions for a total of 9hrs without a problem, same time as using DHW.
Conclusion
Water in the gas main external to my property caused some contamination of the gas valve filter. This in turn caused a reduction in flow/pressure supplied to the gas valve which led to a drop in supply pressure of 1mb. Whilst not a problem to the maximum pressure it was a problem to the minimum required pressure of 2.5mb, pressure actually measured at 1.5mb. I estimate that 4% loss of flow through the gas valve filter would lead to a 1mb drop in pressure.
Suggestion
Baxi should make the filter a servicable, replacable part so it can be checked and/or replaced during annual service.
Baxi should enhance their troubleshooting guide to indicate checking min pressure when any flame/burner issues are being considered.

Thanks again to all who helped me think this issue through.

 

[mickyq]

bronzino i took the boiler cover off to change the pressure switch. im not gas safe registered. have I done something illeagal or unsafe?

 

[GQuigley67]

you shouldnt be working on boilers if your not competent to do so i.e GSR, if you are competent and not GSR you can work on your own boiler but not anyone elses

 

[dles1966]

Final update - I've now run the CH on 3 seperate occassions for a total of 9hrs without a problem, same time as using DHW.
Conclusion
Water in the gas main external to my property caused some contamination of the gas valve filter. This in turn caused a reduction in flow/pressure supplied to the gas valve which led to a drop in supply pressure of 1mb. Whilst not a problem to the maximum pressure it was a problem to the minimum required pressure of 2.5mb, pressure actually measured at 1.5mb. I estimate that 4% loss of flow through the gas valve filter would lead to a 1mb drop in pressure.
Suggestion
Baxi should make the filter a servicable, replacable part so it can be checked and/or replaced during annual service.
Baxi should enhance their troubleshooting guide to indicate checking min pressure when any flame/burner issues are being considered.

Thanks again to all who helped me think this issue through.

Hi quietman, I have a very similar problem, however did you happen to notice if the "burner on" neon lit when you had the fault? as mine does not yet it does light then flame goes out after 9 seconds?

I suspect low flow/pressure, but might be caused by the filter being blocked or at least filthy. Or I also suspect the modulator.

I will need to try the same as you with the "U" tube connected.