Baxi 100/2 HE Plus ignition lockout problem

[rivergo1d]

Hi
First off, I'm not a RGI, just a homeowner, and I have a return visit booked with Baxi for after the weekend, so I'm not attempting a DIY repair. But because the problem is intermittent and the first visit did not solve the problem, I'd appreciate any advice from those with experience so that I can give the repairer as much useful info as possible if the fault is not showing when he turns up.

On the first visit, the condensate trap, burner assembly, combustion box door and gas valve were changed. Since then the boiler has tripped 3 or 4 times in the space of a week.

On pressing the reset button, I've witnessed two kinds of behaviour:-
1. The ignition sequence starts with the two normal mechanical clunks occur, but the gentle whoosh of the flame does not follow. This repeated twice, and on the third attempt, the green ignition light faltered and then stayed on, and the gentle whooshing could be heard - it took a second or two longer for the flame to light on that third attempt than I have heard it taken in the past.
2a. On another occasion, the two normal mechanical clunks occurred, followed by a lot of rapid clicks, several times per second (spark generator?). The gentle whoosh of the flame began, but then the boiler aborted the ignition sequence a few seconds later.
2b. On the next attempt in that sequence, the two normal mechanical clunks occurred, followed by even more rapid clicks, and then it ignited with a "thud" and stayed lit.

Does anyone have any views on what all this may mean? I understand if people may not wish to get involved as there is a re-repair booked for next week, but I feel it could be useful for those plagued with intermittent faults in terms of narrowing down which symptoms to highlight or look for if the RGI cannot witness them himself.

 

[hertsboilers]

It is a right choice to get Baxi their own engineers involved for this boiler. An intermittent ignition lockout is a normal operation status of this boiler! I do boiler repairs, but I regard this boiler as the most difficult boiler to repair with, particularly for an intermittent ignition lockout.

Even you fix it this time, it might come back again.

 

[rivergo1d]

So the pcb was replaced but the fault persists.... No audible spark clicking.

 

[aptsys]

It is a right choice to get Baxi their own engineers involved for this boiler. An intermittent ignition lockout is a normal operation status of this boiler! I do boiler repairs, but I regard this boiler as the most difficult boiler to repair with, particularly for an intermittent ignition lockout.

Even you fix it this time, it might come back again.

I often hear this for some of the Baxi boilers. What's the design flaw that they seem to have?

 

[tango2]

I had the same problem with a Baxi 100/2 HE Plus. After going round the usual loop of replacing the combustion box door sealing strips, the thermostats, the fan gasket, the high voltage harness, the spark and temperature electrodes, the burner and gasket and having the PCB unit professionally checked out exactly the same fault was still there! So I decided to carry out a further investigation using an oscilloscope connected to the temperature electrode, the one fed from a pair of white wires. On switching on but before ignition a 50Hz sinusoidal waveform of about 100 volts peak to peak amplitude was observed, with slight odd-order (symmetrical) distortion. When the boiler fired the amplitude dropped by about 15% and was superimposed with a small amount of random noise and transients from the combustion process. The circuit proved to be of very high impedance, since inserting a 2.2 megohm resistor in series with the temperature electrode made no difference at all, but when the oscilloscope input was switched from AC to DC the boiler tripped out despite a 10 to 1 attenuating probe being in use. It seemed that the remedy did not lie in adding either series or parallel resistance. I began to suspect that the random noise observed earlier was the root cause of the problem, and that a suitable shunt capacitor might be the cure. The capacitor decided upon after trying a range of values was a 2.2nF (2200pF or 0.0022uF) ceramic rated at 400V, which cleans up the sinusoidal wave in both modes considerably without affecting the overall amplitude. This cured the numerous startup attempts and the lockout problem completely, although it still starts with quite an audible 'womp' when hot. The capacitor bypasses transients in the same way as the suppression capacitor used with a motor vehicle ignition coil.