baxpoti.. baxi 100HE plus problems.

[scatmanjohn]

baxpoti or anyone who knows these lovely boilers

I went to a baxi 100he plus with along list off problem.

Burner cracked all the way down one side.

combustion door seal half missing

condensate trap full of what looked like wet bog roll

fan was working when i took it out but not when i put it back in 30 mins later.

Anyway all that is sorted.


However...ever so often ( i saw it do it twice in an hour) it will lockout because the flame is lifting off the burner and going out.

gas inlet pressure is 19.5 mbar

I am suspecting the gas valve but was wondering if this model has one of them gas valve leads with the rectifier hidden in the plug and if so can this cause this type of fault.

Any thoughts appreciated

 

[Agile]

Not a model I go to regularly I am pleased to say!

However, normally a failure of a rectifier diode would be final and never intermittent!

I suppose there could be an intermittent contact within the encapsulated part but I seem to be the only one to disect components to investigate the exact cause of failures.

I understand they a failed diode can often take out the PCB just to be helpful in selling spare parts!

If the flame is lifting off then I would suspect the mixture settings.

Tony

 

[scatmanjohn]

Evening Tony,

I am leaning towards the gas valve sticking. It will run fine for ages on both heating and hot water, modulating without any signs of the fault.

co2 9.6% approx co 180ppm.

Now and again on ignition the fault will occur.

The faults i have had before with the gas valve lead has, like you suggested, meant a total failure.

Intermittant faults make my bum itch

 

[Agile]

Is it locking out after modulating down?

If so what about min gas rate setting?

Or flame detection electrode positioning or leaks lead or high res leads/connections?

If locking out on startup the what about a sticking meter regulator?

Tony

 

[scatmanjohn]

No its not when it modulates down, just when it first fires up.

I don't think the electrodes or leads are a problem.

Its locking out because the flame lifts off the burner. (sometimes)

 

[Agile]

No its not when it modulates down, just when it first fires up.

Weak mixture, too little gas? Sticking meter regulator then?

Does it still do it with gas cooker on full?

Tony

 

[gazthepottertonengineer]

Tony is right if resistor goes in Lead it would be a permanent failure and it sounds like the air to gas ratio mixture is out of calobration which means putting in a new gas valve as you cannot adjust them

also check that the burner is seated properly as i asssume you fitted anew one and there are little lugs which can stop it from sitting properly on the gasket

 

[scatmanjohn]

Cheers gaz ...i will double check the burner but am pretty sure its on right.

If it was not on correctly why would it only do it now and again?

 

[baxpoti]

Check the flue length and suitability, correct burner fitted, gas pipe is fully into venturi and gas rate the appliance.

Does it plume like a steam train going flat out?

Was/is the condensate siphon/pipework blocked?

What's the gas inlet pressure when running at max rate?

and it's nothing to do with the gas valve lead (famous last words)

 

[scatmanjohn]

Check the flue length and suitability, correct burner fitted, gas pipe is fully into venturi and gas rate the appliance.

All present and correct sir

Does it plume like a steam train going flat out?

It does actually, but then again it was a bit nippy outside the last time i was there.

What's the gas inlet pressure when running at max rate?

Its 19.5 mbar and doesn't really move at all.

I haven't
been able the measure it when the fault occurs (they never do it when you want then to)

and it's nothing to do with the gas valve lead (famous last words)

But could it be the gas valve not lifting on initial ignition.

 

[namsag]

Peronally i would be looking at flue seals fan and anything after burner.

 

[baxpoti]

Does it plume like a steam train going flat out?

It does actually, but then again it was a bit nippy outside the last time i was there

Check the heat exchanger for condense leaking back into the burner chamber, if so it's heat ex out and re do the seals, new seals and a fine bead of high temp silicone sealer.