baxi 105e combi cutting out every 15 seconds

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i have a baxi 105e combi boiler. the problem is when i turn on the hot water it fires up and the l.e.d's go all the way up to 80 degrees then it cuts out. This is in hot water mode. when i turn the dhw down to min it comes through warm then cold, if i turn it up to half way it gets very hot for about 10 seconds then lukewarm for 10 seconds and so on.
No faults lights come on and i have changed the plate heat exchanger , changed the dhw temp sensor, changed the safety thermostat, and checked the diaphram for any damage. It fires up ok fan and pump run ok but only for about 20 seconds before it cuts out , then after 10 seconds it fires up again. Could it be a gas problem, maybe a blockage, debris in the pipe or wrong gas pressure. appreciate any help i can get. darren
 
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Needs a new PCB.
Fan kicks in, operates the air pressure switch which trips a relay on the board, which turns the fan off, which drops the voltage from the APS, which resets the relay, which puts power back to the fan, which operates the APS which trips a relay, which turns the fan off, which drops the voltage from the APS, which resets the relay, which puts power back to the fan, which operates the APS which trips a relay, which turns the fan off.......Stop cooking pot! Stop! :rolleyes:
 
Sounds like a blockage to me.

Can't see why a PCB with a faulty fan relay might cause these temperature problems...
 
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Can't see why a PCB with a faulty fan relay might cause these temperature problems...

I understood the OP as being that the LED's went to 80 degrees, and not the boiler.
The LED's going up to 80, is part of the start up sequence; Then, if there was a fault, the respective LED would indicate the fault. The start up sequence and self test, does not show a fault, as the boiler does not get up to temperature, but the fan works, then the APS works, then the fan stops and powers off the APS...... That to me says that it is the PCB.
Perhaps I misunderstood.
Mark :)
 
Ah I see. The way I interpreted it is that the boiler is getting up to 80C rapidly, especially when he mentioned hot then luke warm water. Maybe not! We'll see when the OP posts back.
 
looking at what you have feked about with..
You have changed the DHW sensor but have you changed The main CH sensor as this works on both CH and HW
 
hello everyone, thanks for all your replys. reckon i might go down the new pcb route. surely i would get a fault light if pcb was ok and it was another problem. ps it does it on the heating as well. i have checked the air switch tubes all ok.
 

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