Baxi 105e - Burner re-ignition.

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Lancashire
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Hi. I've got a problem with a Baxi 105e that has stumped me. When running the DHW the burner ignites for around 12secs then goes out. Shortly re-ignites for 12 secs again and then goes out. This will repeat as long as the DHW is being called for. It also happens on the CH once the rads are up to temp. There are no lights flashing to indicate any warnings or faults either.
I have changed both temp sensors, flame sensing probe, checked the incoming power supply and all the obvious ones. I'm down to the problem being either the PCB, the plate heat exchanger requiring cleaning or the gas valve perhaps.
Has anyone ever come across this type of fault before and could you please help me out if you have?
Many thanks. Nick
 
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could be a few things,
min gas pressure,
blocked return filter,
flue/fan/venturi problems
 
Hi. Thank you for a quick reply.
The working pressure is 17.5mbar and the burner pressure is 13.5 mbar.
There is 240v to the pressure switch and the fan is operating in sequence as expected with 240v there also.
The gas valve coil is registering 1v dc when burner is on.
I hope this makes sense.
Thank you. Nick
 
What is the min gas pressure "when the gas valve modulates down to low rate"
 
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Hi. The gas pressure stays at a constant 13.5 mbar whilst the burner is on which is only for 12 secs at a time.
Hope this helps. Thanks Nick
 
Well in that case, this looks like a circulation problem: boiler is cutting off on overheat before the main flow temp sensor is modulating the burner. Blocked 2ndary HX?
 
Hi. Thank you. Would this not lock the boiler out completely until it was reset? Or would it just keep knocking off them firing back up?
Thanks again. Nick
 
nomit wouldnt o/heat it would do exactly wot yours is doing now going on and off you could just take it out and give it a good clean that would do that the job until it gets blocked from the crap in the system again anyway :rolleyes:
 
"""The working pressure is 17.5mbar and the burner pressure is 13.5 mbar.
There is 240v to the pressure switch and the fan is operating in sequence as expected with 240v there also.

The gas valve coil is registering 1v dc when burner is on."""

You have not given any information about the background to this apparent fault!

You have not defined which "gas valve coil" only has 1 VDC.

If an idiot has been fiddling then:

The boiler has tried to modulate down and has only 1 v on the mod coil but the min gas setting equals the max so the gas burner pressure does not modulate down and the boiler gets too hot and switches off.

Solution, check and readjust min and max gas valve setting!

It could be the control signal to the mod coil is missing from the mod coil and the idiot has fiddled the settings to "compensate".

If its something else then sorry, its difficult fixing boilers over the internet! Over the phone yes!

Tony
 
Thank you all very much. The problem lay with the gas valve not modulating to low burn rate. Replaced valve and commisioned boiler to correct pressures. Boiler is now working great. Thanks again for all your help.
 

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