Baxi 105e Combi - Safety Thermostat Indicator Flashing

[admarx]

Hi,
I need some help in understanding this issue. The boiler is 3 yrs old and has worked flawlessly over this time both CH & HW. I have recently fitted a 7 day programmer as well as the room stat already installed. All switching and operation appears normal. However, I notice that when either the room stat or the programmer turn off the CH the neon fault indicator for the Safety Thermostat operation flashes constantly. If either control then calls for heat the boiler fires up OK and runs until the CH internal temp is reached at which time the flame turns off and the Safety Thermostat indicator flashes again. Using the reset function makes no difference, turning the boiler electricity supply off does away with the flashing neon until the first time that either a CH or HW cycle occurs. This is also the case if I turn the control switch to HW only. The boiler fires up and provides hot water until the tap is turned off, when the boiler switches off the Safety Thermostat neon flashes again. I have tested the Safety Thermostat and get 0.00ohms when warm or cold, is this correct? I have read posts on the forum about PCB problems, any ideas?

 

[chrishutt]

If the problem dates from you having fitted the programmer, the wiring for this must be number one suspect. Are you absolutely sure that it's wired up correctly? Is it a remote programmer rather than a built-in (to boiler control panel) one? Could you have made a wiring mistake while installing which damaged the boiler PCB?

 

[admarx]

Thanks for your reply. I can't be certain that it is the programmer wiring causing the error. This is the first time this year that the boiler has been used in anger for heating. I have replaced the link between the remote switch connections to rule out a connection issue with the external controls, however this makes no difference. The boiler does still have the built-in mechanical timer fitted - currently set to permanent on to allow the external controls to work. I tried disconnecting this but the boiler refuses to do anything. Should there be a connecting / shorting plug for the vacant terminals? I suppose if the PCB was damaged prior to re-fitting the link I wouldn't be able to tell. Something I have noticed this morning is that when the CH or HW switches off I can hear a relay turn off the flame and almost straight away another relay click which then flashes the Safety Thermostat neon. The fault neon does not seem to intefere with the operation of the boiler in anyway.