problems with a baxi105e instant combi boiler.

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really60

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i have a baxi 105e instant. i should explain that i recently had to have a leak in the boiler fixed. the boiler was drained to allow the repair. i have two problems but suspect they may be related.
problem 1) there is air in the system but i am not able to remove it. it bubbles into radiators - sometimes quite noisily - but when i try to bleed the radiator only water comes out; never any air. the air then seems to go on around the system. it bubbles into another rad. and then later into yet another and so on.
problem 2) when the c/h is on the temp. neons on the boiler all light up as expected and after 80C is reached the flame turns off. then ALL temp neons briefly switch off, the 80C neon (temp sensor) flashes a few times and then all neons come back on. there are sometimes variations on this theme but what i have described is the most common one.

is it possible for the trapped air to be causing a problem for the temp. sensor? whatever the answer, can you help me solve these problems?
 
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the boiler should vent itself from the auto air vent,check if the cap on it is unscrewed
 
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ok, i have found the auto air vent cap. now, do tighten it or unscrew it and if so how much? if i go too far could it fall out?
 
found it. unscrewed it and it fell out. having real problems getting it back in. will system be ok if i leave it out? i've turned everything off for the time being.
 
got it back in - finally. turned system on again and now waiting to see what happens.

thank you bunny for your help so far - now fingers crossed.
 
Back to the fault, its possible that the temperature sensor is going open circuit when its hot.

As its not expensive it might be possible to just replace it and see if it sorts out the problem.

If you wanted to test it then measure the voltage across it which should fall as the boiler warms up. If it was what I suggested then the voltage would jump up suddenly when its hot.

Tony
 
one further point for bunny. if everything now works ok, should i close the auto air vent cap again or leave it open?

thank you for your post agile. i'll see how the air vent solution goes before trying anything else, but if the problem is not fixed i'll try what you suggest.
 
thanks bunny. i've done what i think you meant - that is left the vent cap on but only half screwed down. to start with it seemed to work but now the problem seems to be returning.

similar problems have happened before; three days ago the boiler lights flashed as described above but the burners cycled on and off several times then something 'screeched' (similar to the noise a wet clutch plate on a car will sometimes make), made a few knocking noises and seemed to solve the problem. it worked perfectly. until this morning when the problem returned. and i wrote my problem to DIYnot.

i should add that when i turn rads. up the problem is less likely to happen but when the system has settled down and is just working gently it seems likely to return.
 
does the boiler go to low flame when nearly at full temp?
 
the heating cycle is: -
ignition then to high flame,
after a few seconds to low flame,
then to high flame for the rest of the cycle until a few seconds before turning off when back to low flame.

so in answer to your question - yes.
 
an addition to my last post. i have just noticed that on occasions when the lights don't work properly the boiler does,as usual, go on low flame when nearly at full temp but sometimes very briefly the flame suddenly gets bigger just before it turns off.
when that happens i seem to hear a lot of 'bubbling' noises. it sounds like a mass of tiny bubbles going round the system.
something else that sometimes happens is that as the water is heating one or a few of the temp neons light up, go off, then light again (but they are not flashing in a regular way). just now after all the lights had lit up they all went off, the flame went high, all lights came on again and then the flame went out.
 
D

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