baxi 105e overheat problem

[cdel2005]

hi guys,

i have a baxi 105e and its overheating,the temp neon go up one by one until 80 degrees then lockout, once it cools the boiler fires up again until it reaches 80 degrees,the dhw works as it should no problems the diverter valve and micro switches all work as they should.

*the water in CH pipes/rads is noticeably hotter

*I have changed the thermister with no effect


Im beginning to think its either the PCB or a blocked heat exchanger but not sure hopefully somebody will have experienced this.

is there any way to identify the temp fault?

cheers

[galaxy_plumbing]

try to search on forum. there is a lot of topics about baxi 105

[casaco]

Had the same problem last week, diverter valve stopped the heat going down the flow, only went to the plate to plate, got hot fast and locked out. Check that first. Flow pipe near boiler will get hot due to heat transfer but feel flow pipe about a meter away, if it isn't getting hot the valve has had it.

[buckley plumb]

as others have said in other posts check the heating return filter. remove the front part of the diverter and check the pin is not seized in the back part of the diverter.

ant

[Koogatubac]

I had this exact problem. Found that the DHW sensor wasnt functioning right, changed the sensor. That day it kept doing the same fault.

Customer contacted me 5 days after and said the boilers been great and shes had constant hot water

Next port of call i was going to check the DHW Heat exchanger.

[casaco]

The boiler is working ok on DHW, the Thermistor has been changed, so presumably the fault occurs on heating demand only, so would suspect water not passing through diverter valve to heating circuit, but CH thermistor doesn't know diverter valve is stuck so allows boiler to fire continuously to 80 degrees, boiler shuts down but latent heat exceeds over heat temp at 95 degrees and goes to lock out. simple really.

[Koogatubac]

So the high limit stat sounds like its working if its cutting the boiler out.

Might be worth checking the heat exchanger isnt blocked

[buckley plumb]

The boiler is working ok on DHW, the Thermistor has been changed, so presumably the fault occurs on heating demand only, so would suspect water not passing through diverter valve to heating circuit, but CH thermistor doesn't know diverter valve is stuck so allows boiler to fire continuously to 80 degrees, boiler shuts down but latent heat exceeds over heat temp at 95 degrees and goes to lock out. simple really.

check filter first if hw is ok then could be heating rtn filter

[cdel2005]

the dhw works when on dhw only and ch/dhw

I had this exact problem. Found that the DHW sensor wasnt functioning right, changed the sensor. That day it kept doing the same fault.

Customer contacted me 5 days after and said the boilers been great and shes had constant hot water

Next port of call i was going to check the DHW Heat exchanger.