Baxi 105e CH but no DHW

[roysterC]

Hello everyone,

My CH works fine, but my DHW doesn't. DHW only works when CH is on too. I've gone through and checked my boiler out. The two microswitches work as expected. The pressure is hovering within the correct range. Both the lights to CH and DHW light up when expected. However, the burner light only turns on when CH is on but when CH is off and DHW is needed the boiler fires up the microswitches work correctly however the burner led light does not turn on. I'm not sure if this burner light is an issue but it has led me to think it's either a electronic problem - replace the PCB or a mechanical problem - diverter valve.

I'll be glad if someone can enlighten me.

 

[CountryFan]

I’m confused slightly as you said it fires the boiler up in dhw but burner light doesn’t come on, is this correct?

 

[roysterC]

I’m confused slightly as you said it fires the boiler up in dhw but burner light doesn’t come on, is this correct?

Yes sorry for the confusion. What I meant by firing up is that the boiler makes a whirring noise which means some part of the boiler is reacting to the need for dhw, however the burner does not turn on. There is no flame.

 

[CountryFan]

Yes sorry for the confusion. What I meant by firing up is that the boiler makes a whirring noise which means some part of the boiler is reacting to the need for dhw, however the burner does not turn on. There is no flame.

Sounds as though you have described a diverter issue then. You say the microswitch is ok, but it sounds as though it’s not making full contact. If you place a dhw demand on, the rod pushes out, but probably not all the way. If you do this and then press the microswitch manually with an implement, should fire the boiler up.

 

[roysterC]

And which microswitch, are you referring to. There's a microswitch for the pressure differential valve and for the diverter manifold.

I'd also like to say, I've followed the manuals debugging chart. and through following it. The two final solutions it leads me with is replace gas valve or replace pcb.

If you care to take a look, https://www.acwilgar.co.uk/Boiler-Manual-PDF/Baxi/combi 105E.pdf , page 39 follow until 'burner on illuminated' which the answer to is no -> go to section F

 

[roysterC]

I tested out the microswitch for the pressure differential. The CH was on, the burner light was on. As soon as I turn on the microswitch which tells the boiler to direct water to DHW, the burner will turn off. Once I release the switch the burner turns back on. Any idea if this is normal or how it can be fixed ?

 

[CountryFan]

We don’t know if the fan runs at max speed, if the pump runs, etc. I understand you think it may be the gas valve or pcb but it might not be. The microswitch I’m referring to is the one that triggers the dhw

 

[roysterC]

We don’t know if the fan runs at max speed, if the pump runs, etc. I understand you think it may be the gas valve or pcb but it might not be. The microswitch I’m referring to is the one that triggers the dhw

Yep the microswitch which dictates the flow of water for dhw is what im referring to aswell. It causes the burner to turn off immediately. Even when the CH is on and the burner is already on, as soon as the microswitch is on the burner turns off, but when I release the microswitch the burner immediately turns back on for the CH.

Given this scenario it is no wonder, the burner does not turn on when its just dhw needed and not ch as well.