another 105e problem

[giarc00007]

Hi guys, just been to above boiler (not preheat). boiler keeps locking out to flame failure at totally random times, could be 30 seconds could be 5 mins. Then if i reset boiler and put heating on then open hot tap the boiler will go to lockout but the fan light will flash as well as flame failure. it only happens if control knob is in hw and heating mode, if i turn knob to hw only it is fine. i was thinking pcb. Any advice will be much appreciated.

 

[lame plumber]

cant remember for sure but they rely on the ncts working to fire up, try a new one on the ch side to see if that is failing first, then if not pop in the 2nd hand pcb you carry fm that old 105e you ripped out to check if it is the pcb 🙂

 

[giarc00007]

cant remember for sure but they rely on the ncts working to fire up, try a new one on the ch side to see if that is failing first, then if not pop in the 2nd hand pcb you carry fm that old 105e you ripped out to check if it is the pcb 🙂

thanks lame. would it be a ntc even if its fine when it hw only mode?, also dont have spare pcb unfortunately

 

[REDSAW]

start at the cheap end and work up, handy spres if not

 

[giarc00007]

start at the cheap end and work up, handy spres if not

I know was first thinking sensing electrode or cable. But then when realised it worked fine when switched to hot water only I ruled that out along with thermistors and aps which are the cheapest.

 

[REDSAW]

try swapping them around and see what results are

 

[Billy Bob Bob]

put a multi meter on the ntc,should e 11k cold,however a ntc will not cause the fan light to flash up,if its A SE,would be looking closely at the relay in the pcb after checking fan ,flue and aps function,if a HE version would be looking very closely at the aps and fan if a long flue run

 

[Elgordo]

Had one with same problem last year , try swopping the Nct's to eliminate the bad one . I had to change the APS as well after two hours of head scratching as the contacts were going resistive as against on/off .

 

[giarc00007]

just an update, havn't been able to get back to job but customer has reported back that if they turn the dial to hot water only they can get hot water all day no probs at all, if they turn dial to hot water and heating, the heating will stay on no probs but minute they put a demand for hot water while in heating and hot water mode this is when it locks out. will try changing over ntc's next week.