Baxi 105e Central Heating Constantly on when override at off

[flyingspanner]

Defect: When selector placed at hot water / central heating the boiler is constantly running even though manual over-ride is selected off. It means the timer function cannot be used.

Actions Taken so far:

1) I have verified that the CH Diff PX microswitch working correctly.
2) I have checked Auto Bypass membrane intact.
3) I have reset the system.
4) I have unplugged the timer to PCB to no avail. - Still the same.

Any ideas gentlemen? I am thinking that it maybe the PCB or the divider valve. However I may have missed something fundamental.

Advice appreciated.

Flyingspanner

 

[bengasman]

Did they leave the old timer from the previous boiler in place by any chance?

 

[flyingspanner]

Digital tiimer still there and connected back up but does not have any effect on the operation of the boiler in any way.

Used to work fine, unsure as to what has happened

 

[bengasman]

Digital tiimer still there and connected back up but does not have any effect on the operation of the boiler in any way.

True enough, but it does indicate that the job was done on the cheap. That in turn means that it is likely corners were cut. Result of that being that you can expect all sorts of things like sloppy wiring, poor earth, gunk in system leading to pressure switch, flow switch, dhw switch, diverter sticking, and more fun like that.

 

[flyingspanner]

Obviously dont know, system been installed since we moved in 4 years ago. Worked fine until recently, only problem with system until then was diaphram being required due puncture on the hot water side.

Wiring looks clean, unsure about the earths yet, will have to check.

Just as soon as you turn the selector to both Central heating and Hot water combined then the boiler runs. Regardless of the over-ride on the timer.

Switch goes round. Central heating diff pressure plunger comes up makes switch and heating system comes on.

Just trying to work out what would cause that. Would not probably be something on PCB??? Or would it be a more mechanical fault? 3 way valve?

 

[bengasman]

3 way valve on this model is a bit wonky, quite sensitive to dirt in the system. One of the common problems of sloppy install work. Poxi does not have a great reputation for pcb's, but I don't think this model is too bad.

 

[flyingspanner]

Question is: How do I narrow down the possibilities?

Any tests which can prove either that you konw about?

BTW thanks for the help!

 

[bengasman]

Read through the wiki and faq section. If the info in there is not enough to do it, it's time to call a pro.