Baxi duo tec he24 CH but no hot water, no error code

[agb32]

Hi,
I have a baxi duo-tec he24 which is causing some puzzlement at the moment.
Central heating is working fine.
But direct hot water is not working.
When I turn the tap on - the Hall effect sensor works (red LED). The indicator on the front panel indicating that it recognises water is being drawn lights up.
But the boiler doesn't fire (though of course it does when only CH is needed).

The DHW NTC temperature sensor appears to be fine (resistance about right, and the measured temperature shown on the LCD display is what I would expect).

No error codes are shown.

The diverter valve is working properly.

So - why isn't the boiler firing? Anyone got any ideas?

The only thing I can think of now is the PCB - but that seems to be a bit of a last resort, and an expensive one at that.

The boiler is just over 2 years old, just out of warranty.

 

[Agile]

I cannot totally visualise your boiler model.

However, if its still based on the older Baxi combis then a fault like that could well be the PCB.

I agree that you seem to have covered all the typical issues ( apart from measuring the CH sensor resistance ).

It also worrying to me when people here say that something is fine because I dont know what they think constitutes being fine!

Tony

 

[CBF]

prob like when your lady says "I'm fine"

 

[Agile]

You mean like she wants something?

 

[engineerman]

have you checked the pipework to see if any of the pipes are getting hot?

 

[agb32]

The pipes are getting hot in CH mode (when the boiler is firing), but not getting hot in DHW mode (because the boiler doesn't fire).
Temperature readings from the CH NTC are what I expect them to be.
By working fine, I mean that heat is getting to radiators at the correct temperature when it is required (i.e. when timer is set and thermostat dips below the set point).

Thanks...

 

[Baxmax]

Change the dhw ntc thermister and it will work

 

[Agile]

Hi,

The DHW NTC temperature sensor appears to be fine (resistance about right, and the measured temperature shown on the LCD display is what I would expect).

But even though I questioned him about it he is quite sure that the DHW ntc is "Fine" !

 

[agb32]

Hi,
I assumed that because the resistance measurement is okay and because the temperature measurement given is sensible, then the DHW NTC sensor isn't at fault.

But - maybe my assumptions are wrong? Have you come across this problem before? If it was at fault then it should give the E50 error?

So, are you sure that changing the DHW NTC sensor will get it working?

 

[doitall]

Change the dhw ntc thermister and it will work

About 20 posters have told him that over several forums, the OP is looking for someone to tell him to change the diverter valve and PCB.

 

[agb32]

ok - I'll try changing the NTC... and post back if it works...
I suppose I've been reluctant because I can't understand why it should work (and I like to understand something before I do it!)!

 

[agb32]

By thermister, I presume you mean this:
http://www.plumbcenter.co.uk/en/heating-parts/domestic-boiler-parts/baxi-5114725-ntc-sensor-34608

 

[Agile]

That looks like it but I cannot definately say its the correct one for your boiler!

They will search against your boiler model to confirm.

So you are a multiple posted then? Filling up different forums with all the same questions? Mostly the same experts answer!

Tony

 

[Baxmax]

Yes correct sensor, the fault code will show if it is faulty not if it is out of calibration.
Any way if we are all wrong its far cheaper than all the other parts you mention.

 

[agb32]

Hi all,
Changed the DHW NTC, and indeed - that has fixed it, so thanks a lot, and sorry for my doubt...
I've made a donation to Donnas Dream house as suggested on another forum, since it saved me a fair packet for a new PCB, and someone to fit it, that the Baxi helpline had recommended.

If anyone is interested in why it worked, here is my reasoning...
The temperature displayed on the user panel, which was giving sensible readings, is measured by the CH NTC only, even when in DHW mode (which is sensible, since the CH NTC is measuring the water temperature in the heat exchanger). Thus, there is no way for a user to know what the temperature of the DHW NTC is. The DHW NTC was failing, resistance decreasing gradually (which is equivalent to a higher temperature) - thus the boiler thought the water was already hot enough. But since the resistance was still in an allowed range, the boiler wasn't giving an error message - it just thought the water was hotter than it really was.

I just wish the baxi helpline had told me this...

Anyway, thanks again, and I hope this helps someone in the future...